Compound, light-emitting element, light-emitting device, electronic device, and lighting device

ABSTRACT

To provide a novel compound which can be used as a host material in which a light-emitting substance is dispersed. To provide a light-emitting element having a long lifetime. A compound represented by General Formula (G0). In the formula, A 1  represents a dibenzo[f,h]quinoxalinyl group, A 2  represents a benzo[b]naphtho[2,3-d]furanyl group, and Ar represents an arylene group having 6 to carbon atoms. The dibenzo[f,h]quinoxalinyl group, the benzo[b]naphtho[2,3-d]furanyl group, and the arylene group are separately unsubstituted or substituted by any one of an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, and an aryl group having 6 to 13 carbon atoms.

BACKGROUND OF THE INVENTION

1. Field of the Invention

One embodiment of the present invention relates to a compound, alight-emitting element utilizing electroluminescence (EL) (thelight-emitting element is also referred to as an EL element), alight-emitting device, an electronic device, and a lighting device.

Note that one embodiment of the present invention is not limited to theabove technical field. One embodiment of the invention disclosed in thisspecification and the like relates to an object, a method, and amanufacturing method. Moreover, one embodiment of the present inventionrelates to a process, a machine, manufacture, or a composition ofmatter. Specifically, examples of the technical field of one embodimentof the present invention disclosed in this specification include asemiconductor device, a display device, a light-emitting device, a powerstorage device, a memory device, an electronic device, a lightingdevice, a method for driving any of them, and a method for manufacturingany of them.

2. Description of the Related Art

In recent years, a light-emitting element using an organic compound as alight-emitting substance (the light-emitting element is also referred toas an organic EL element) has been actively researched and developed. Ina basic structure of the light-emitting element, a layer containing alight-emitting substance is provided between a pair of electrodes.Voltage application to this element causes the light-emitting substanceto emit light.

The light-emitting element is a self-luminous element and thus hasadvantages over a liquid crystal display, such as high visibility of thepixels and no need of backlight, and is considered to be suitable as aflat panel display element. Another major advantage of thelight-emitting element is that it can be fabricated to be thin andlightweight. Besides, the light-emitting element has an advantage ofquite high response speed.

Since the light-emitting element can be formed in a film form, planarlight emission can be provided; thus, a large-area element can be easilyformed. This feature is difficult to obtain with point light sourcestypified by incandescent lamps and LEDs or linear light sources typifiedby fluorescent lamps. Thus, the light-emitting element also has greatpotential as a planar light source applicable to a lighting device andthe like.

In the case of a light-emitting element in which a layer containing anorganic compound used as a light-emitting substance is provided betweena pair of electrodes, by applying a voltage to the element, electronsfrom a cathode and holes from an anode are injected into the layercontaining the organic compound and thus a current flows. The injectedelectrons and holes then lead the organic compound to its excited state,so that light emission is provided from the excited organic compound.

The excited state formed by an organic compound can be a singlet excitedstate or a triplet excited state. Light emission from the singletexcited state (S*) is called fluorescence, and light emission from thetriplet excited state (T*) is called phosphorescence. The statisticalgeneration ratio thereof in the light-emitting element is considered tobe S*:T*=1:3.

At room temperature, a compound capable of converting a singlet excitedstate into light emission (hereinafter, referred to as a fluorescentcompound) exhibits only light emission from the singlet excited state(fluorescence), and light emission from the triplet excited state(phosphorescence) cannot be observed. Accordingly, the internal quantumefficiency (the ratio of the number of generated photons to the numberof injected carriers) of a light-emitting element including afluorescent compound is assumed to have a theoretical limit of 25%, onthe basis of S*:T*=1:3.

In contrast, a compound capable of converting a triplet excited stateinto light emission (hereinafter, referred to as a phosphorescentcompound) exhibits light emission from the triplet excited state(phosphorescence). Furthermore, since intersystem crossing (i.e.,transition from a singlet excited state to a triplet excited state)easily occurs in a phosphorescent compound, the internal quantumefficiency can be theoretically increased to 100%. That is, higheremission efficiency can be achieved than using a fluorescent compound.For this reason, light-emitting elements using a phosphorescent compoundhave been under active development recently so that high-efficiencylight-emitting elements can be achieved.

When a light-emitting layer of a light-emitting element is formed usingthe phosphorescent compound described above, in order to inhibitconcentration quenching or quenching due to triplet-triplet annihilationof the phosphorescent compound, the light-emitting layer is usuallyformed such that the phosphorescent compound is dispersed in a matrix ofanother compound. Here, the compound serving as the matrix is calledhost material, and the compound dispersed in the matrix, such as aphosphorescent compound, is called guest material.

When a phosphorescent compound is a guest material, a host materialneeds to have higher triplet excitation energy (energy differencebetween a ground state and a triplet excited state) than thephosphorescent compound.

Furthermore, since singlet excitation energy (energy difference betweena ground state and a singlet excited state) is higher than tripletexcitation energy, a substance that has high triplet excitation energyalso has high singlet excitation energy. Thus, the above substance thathas high triplet excitation energy is also effective in a light-emittingelement using a fluorescent compound as a light-emitting substance.

Studies have been conducted on compounds having dibenzo[f,h]quinoxalinerings, which are examples of the host material used when aphosphorescent compound is a guest material (e.g., see Patent Documents1 and 2).

REFERENCE Patent Document [Patent Document 1] PCT InternationalPublication No. 03/058667 [Patent Document 2] Japanese Published PatentApplication No. 2007-189001 SUMMARY OF THE INVENTION

In improving element characteristics of a light-emitting element, thereare many problems which depend on a substance. Therefore, improvement inan element structure, development of a substance, and the like have beencarried out in order to solve the problems. Development oflight-emitting elements leaves room for improvement in terms of emissionefficiency, reliability, cost, and the like.

For practical use of a display or lighting which uses a light-emittingelement, a long lifetime of the light-emitting element has beenrequired.

In view of the above, an object of one embodiment of the presentinvention is to provide a novel compound. An object of one embodiment ofthe present invention is to provide a novel compound which can be usedin a light-emitting element as a host material in which a light-emittingsubstance is dispersed. An object of one embodiment of the presentinvention is to provide a novel compound that enables a light-emittingelement to have high reliability. An object of one embodiment of thepresent invention is to provide a compound whose film quality is high.An object of one embodiment of the present invention is to provide acompound with high heat resistance.

An object of one embodiment of the present invention is to provide alight-emitting element with high emission efficiency. An object of oneembodiment of the present invention is to provide a light-emittingelement with a low drive voltage. An object of one embodiment of thepresent invention is to provide a light-emitting element having a longlifetime. An object of one embodiment of the present invention is toprovide a light-emitting element with high heat resistance. An object ofone embodiment of the present invention is to provide a novellight-emitting element.

An object of one embodiment of the present invention is to provide ahighly reliable light-emitting device, a highly reliable electronicdevice, or a highly reliable lighting device using the light-emittingelement. An object of one embodiment of the present invention is toprovide a light-emitting device, an electronic device, or a lightingdevice with low power consumption using the light-emitting element.

Note that the descriptions of these objects do not disturb the existenceof other objects. In one embodiment of the present invention, there isno need to achieve all the objects. Other objects will be apparent fromand can be derived from the description of the specification, thedrawings, the claims, and the like.

One embodiment of the present invention is a compound represented byGeneral Formula (G0).

A¹-Ar-A²  (G0)

In General Formula (G0), A¹ represents a dibenzo[f,h]quinoxalinyl group,A² represents a benzo[b]naphtho[2,3-d]furanyl group, and Ar representsan arylene group having 6 to 25 carbon atoms. Thedibenzo[f,h]quinoxalinyl group, the benzo[b]naphtho[2,3-d]furanyl group,and the arylene group are separately unsubstituted or substituted by anyone of an alkyl group having 1 to 6 carbon atoms, a cycloalkyl grouphaving 3 to 6 carbon atoms, and an aryl group having 6 to 13 carbonatoms.

One embodiment of the present invention is a compound represented byGeneral Formula (G1).

In General Formula (G1), one of R⁷ to R¹⁰ represents a substituentrepresented by General Formula (G1-1); R¹ to R⁶ and the others of R⁷ toR¹⁰ separately represent any one of hydrogen, an alkyl group having 1 to6 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, and anaryl group having 6 to 13 carbon atoms; A represents adibenzo[f,h]quinoxalinyl group; and Ar represents an arylene grouphaving 6 to 25 carbon atoms. The dibenzo[f,h]quinoxalinyl group, thearyl group, and the arylene group are separately unsubstituted orsubstituted by any one of an alkyl group having 1 to 6 carbon atoms, acycloalkyl group having 3 to 6 carbon atoms, and an aryl group having 6to 13 carbon atoms.

One embodiment of the present invention is a compound represented byGeneral Formula (G2).

In General Formula (G2), R¹ to R⁹ separately represent any one ofhydrogen, an alkyl group having 1 to 6 carbon atoms, a cycloalkyl grouphaving 3 to 6 carbon atoms, and an aryl group having 6 to 13 carbonatoms; A represents a dibenzo[f,h]quinoxalinyl group; and Ar representsan arylene group having 6 to 25 carbon atoms. Thedibenzo[f,h]quinoxalinyl group, the aryl group, and the arylene groupare separately unsubstituted or substituted by any one of an alkyl grouphaving 1 to 6 carbon atoms, a cycloalkyl group having 3 to 6 carbonatoms, and an aryl group having 6 to 13 carbon atoms.

One embodiment of the present invention is a compound represented byGeneral Formula (G3).

In General Formula (G3), R¹ to R⁹ and R¹¹ to R¹⁹ separately representany one of hydrogen, an alkyl group having 1 to 6 carbon atoms, acycloalkyl group having 3 to 6 carbon atoms, and an aryl group having 6to 13 carbon atoms, and Ar represents an arylene group having 6 to 25carbon atoms. The aryl group and the arylene group are separatelyunsubstituted or substituted by any one of an alkyl group having 1 to 6carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, and an arylgroup having 6 to 13 carbon atoms.

One embodiment of the present invention is a light-emitting elementhaving any of the compounds with the above structures between a pair ofelectrodes.

One embodiment of the present invention is a light-emitting elementwhich includes a layer containing a compound between a pair ofelectrodes and in which the compound has a dibenzo[f,h]quinoxalineskeleton and a benzo[b]naphtho[2,3-d]furan skeleton.

One embodiment of the present invention is a light-emitting elementwhich includes a layer containing a compound between a pair ofelectrodes and in which the compound is a compound where adibenzo[f,h]quinoxaline skeleton and a benzo[b]naphtho[2,3-d]furanskeleton are bonded through an arylene skeleton.

One embodiment of the present invention is a light-emitting deviceincluding the above-described light-emitting element in a light-emittingportion. For example, a light-emitting device of one embodiment of thepresent invention may include the above light-emitting element and atransistor or a substrate. One embodiment of the present invention is anelectronic device including the light-emitting device in a displayportion. For example, an electronic device of one embodiment of thepresent invention may include the above light-emitting device and amicrophone, a speaker, or an external connection terminal. Oneembodiment of the present invention is a lighting device including thelight-emitting device in a light-emitting portion. For example, alighting device of one embodiment of the present invention may includethe above light-emitting device and a support, a housing, or a cover.

Note that the light-emitting device in this specification includes, inits category, a display device using a light-emitting element.Furthermore, the light-emitting device may be included in a module inwhich a light-emitting element is provided with a connector such as ananisotropic conductive film or a tape carrier package (TCP), a module inwhich a printed wiring board is provided at the end of a TCP, and amodule in which an integrated circuit (IC) is directly mounted on alight-emitting element by a chip on glass (COG) method. Thelight-emitting device may be included in lighting equipment or the like.

A compound represented by General Formula (G4), which is used insynthesis of the compound of one embodiment of the present invention, isalso one embodiment of the present invention.

In General Formula (G4), R¹ to R⁹ separately represent any one ofhydrogen, an alkyl group having 1 to 6 carbon atoms, a cycloalkyl grouphaving 3 to 6 carbon atoms, and an aryl group having 6 to 13 carbonatoms, and R¹⁰ represents any one of chlorine, boron, iodine, a boronicacid group, and an organoboron group. The aryl group is unsubstituted orsubstituted by any one of an alkyl group having 1 to 6 carbon atoms, acycloalkyl group having 3 to 6 carbon atoms, and an aryl group having 6to 13 carbon atoms.

A compound represented by Structural Formula (201), which is used insynthesis of the compound of one embodiment of the present invention, isalso one embodiment of the present invention.

One embodiment of the present invention makes it possible to provide anovel compound. One embodiment of the present invention makes itpossible to provide a novel compound which can be used in alight-emitting element as a host material in which a light-emittingsubstance is dispersed. One embodiment of the present invention makes itpossible to provide a novel compound that enables a light-emittingelement to have high reliability. One embodiment of the presentinvention makes it possible to provide a compound whose film quality ishigh. One embodiment of the present invention makes it possible toprovide a compound with high heat resistance.

One embodiment of the present invention makes it possible to provide alight-emitting element with high emission efficiency. One embodiment ofthe present invention makes it possible to provide a light-emittingelement with a low drive voltage. One embodiment of the presentinvention makes it possible to provide a light-emitting element having along lifetime. One embodiment of the present invention makes it possibleto provide a light-emitting element with high heat resistance. Oneembodiment of the present invention makes it possible to provide a novellight-emitting element.

One embodiment of the present invention makes it possible to provide ahighly reliable light-emitting device, a highly reliable electronicdevice, or a highly reliable lighting device using the light-emittingelement. One embodiment of the present invention makes it possible toprovide a light-emitting device, an electronic device, or a lightingdevice with low power consumption using the light-emitting element.

Note that the description of these effects does not disturb theexistence of other effects. One embodiment of the present invention doesnot necessarily achieve all the above effects. Other effects will beapparent from and can be derived from the description of thespecification, the drawings, the claims, and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1D each illustrate an example of a light-emitting element ofone embodiment of the present invention.

FIGS. 2A and 2B illustrate an example of a light-emitting device of oneembodiment of the present invention.

FIGS. 3A to 3C illustrate examples of a light-emitting device of oneembodiment of the present invention.

FIGS. 4A to 4E illustrate examples of an electronic device.

FIGS. 5A to 51 illustrate examples of an electronic device.

FIGS. 6A and 6B illustrate examples of a lighting device.

FIGS. 7A and 7B show ¹H NMR charts of8-chlorobenzo[b]naphtho[2,3-d]furan.

FIGS. 8A and 8B show ¹H NMR charts of2-[3′-(benzo[b]naphtho[2,3-d]furan-8-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline(abbreviation: 2mBnf(II)BPDBq).

FIGS. 9A and 9B show an absorption spectrum and an emission spectrum ofa toluene solution of 2mBnf(II)BPDBq.

FIGS. 10A and 10B show an absorption spectrum and an emission spectrumof a thin film of 2mBnf(II)BPDBq.

FIGS. 11A and 11B show results of LC-MS analysis of 2mBnf(II)BPDBq.

FIG. 12 illustrates light-emitting elements in Examples.

FIG. 13 is a graph showing voltage-luminance characteristics of alight-emitting element in Example 2.

FIG. 14 is a graph showing luminance-current efficiency characteristicsof a light-emitting element in Example 2.

FIG. 15 is a graph showing voltage-current characteristics of alight-emitting element in Example 2.

FIG. 16 is a graph showing an emission spectrum of a light-emittingelement in Example 2.

FIG. 17 shows results of a reliability test of a light-emitting elementin Example 2.

FIG. 18 is a graph showing voltage-current characteristics of alight-emitting element in Example 3.

FIG. 19 is a graph showing luminance-external quantum efficiencycharacteristics of a light-emitting element in Example 3.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be described in detail withreference to the drawings. Note that the present invention is notlimited to the following description, and it is easily understood bythose skilled in the art that various changes for embodiments anddetails can be made without departing from the spirit and scope of theinvention. Therefore, the present invention should not be construed asbeing limited to the description in the following embodiments.

Note that in the structures of the invention described below, the sameportions or portions having similar functions are denoted by the samereference numerals in different drawings, and description of suchportions is not repeated. Furthermore, the same hatching pattern isapplied to portions having similar functions, and the portions are notespecially denoted by reference numerals in some cases.

In addition, the position, size, range, or the like of each structureillustrated in drawings and the like is not accurately represented insome cases for easy understanding. Therefore, the disclosed invention isnot necessarily limited to the position, the size, the range, or thelike disclosed in the drawings and the like.

Note that the terms “film” and “layer” can be interchanged with eachother depending on the case or circumstances. For example, the term“conductive layer” can be changed into the term “conductive film” insome cases. In addition, the term “insulating film” can be changed intothe term “insulating layer” in some cases.

Embodiment 1

In this embodiment, a compound of one embodiment of the presentinvention is described.

One embodiment of the present invention is a compound in which adibenzo[f,h]quinoxaline skeleton and a benzo[b]naphtho[2,3-d]furanskeleton are bonded through an arylene skeleton.

A dibenzo[f,h]quinoxaline skeleton has a planar structure. A compoundhaving a planar structure is easily crystallized. A light-emittingelement using a compound that is easily crystallized has a shortlifetime. However, the compound of one embodiment of the presentinvention has a sterically bulky structure since abenzo[b]naphtho[2,3-d]furan skeleton is bonded to adibenzo[f,h]quinoxaline skeleton through an arylene skeleton. Thecompound of one embodiment of the present invention is not easilycrystallized, which can inhibit a reduction in lifetime of alight-emitting element. By including a benzo[b]naphtho[2,3-d]furanskeleton, in which a benzene ring and a naphthalene ring are condensedwith a furan skeleton, and a dibenzo[f,h]quinoxaline skeleton, in whichtwo benzene rings are condensed with a quinoxaline skeleton, thecompound of one embodiment of the present invention has extremely highheat resistance, and when the compound is used in a light-emittingelement, the light-emitting element can have high heat resistance and along lifetime.

When a compound that cannot easily accept electrons or holes is used asa host material in a light-emitting layer, the regions of electron-holerecombination concentrate on an interface between the light-emittinglayer and a different layer, leading to a reduction in lifetime of alight-emitting element. Here, the compound of one embodiment of thepresent invention can easily accept electrons and holes since thecompound has a dibenzo[f,h]quinoxaline skeleton as an electron-transportskeleton and a benzo[b]naphtho[2,3-d]furan skeleton as a hole-transportskeleton. Accordingly, by the use of the compound of one embodiment ofthe present invention as the host material of the light-emitting layer,electrons and holes presumably recombine in a wide region of thelight-emitting layer and it is possible to inhibit a reduction inlifetime of the light-emitting element.

As compared to extension of a conjugated system in a compound in which adibenzo[f,h]quinoxaline skeleton and a benzo[b]naphtho[2,3-d]furanskeleton are directly bonded, extension of a conjugated system in thecompound of one embodiment of the present invention in which the twoskeletons are bonded through an arylene group is small; accordingly,reductions in band gap and triplet excitation energy can be prevented.The compound of one embodiment of the present invention is alsoadvantageous in that its heat resistance and film quality are high.Specifically, a thin film of the compound of one embodiment of thepresent invention suffers only a small change in shape (e.g.,aggregation is not easily caused even under the air and crystallizationis not easily caused even under high temperatures).

The compound of one embodiment of the present invention has a wide bandgap. Accordingly, the compound can be favorably used as a host material,in which a light-emitting substance is dispersed, of a light-emittinglayer in a light-emitting element. Furthermore, since the compound ofone embodiment of the present invention has triplet excitation energyhigh enough to excite a phosphorescent compound emitting light in awavelength range from red to green, the compound can be favorably usedas a host material in which the phosphorescent compound is dispersed.

When the triplet excitation energy of a host material is too high, theadverse effects of a quenching factor increase and a light-emittingelement easily deteriorates in some cases. With the use of the compoundof one embodiment of the present invention, a light-emitting elementthat is less likely to be affected by the quenching factor and does noteasily deteriorate can be provided.

Furthermore, since the compound of one embodiment of the presentinvention has a high electron-transport property, the compound can besuitably used as a material for an electron-transport layer in alight-emitting element.

Thus, the compound of one embodiment of the present invention can besuitably used as a material for an organic device such as alight-emitting element or an organic transistor.

One embodiment of the present invention is a compound represented byGeneral Formula (G0).

A¹-Ar-A²  (G0)

In General Formula (G0), A¹ represents a dibenzo[f,h]quinoxalinyl group,A² represents a benzo[b]naphtho[2,3-d]furanyl group, and Ar representsan arylene group having 6 to 25 carbon atoms. Thedibenzo[f,h]quinoxalinyl group, the benzo[b]naphtho[2,3-d]furanyl group,and the arylene group are separately unsubstituted or substituted by anyone of an alkyl group having 1 to 6 carbon atoms, a cycloalkyl grouphaving 3 to 6 carbon atoms, and an aryl group having 6 to 13 carbonatoms.

One embodiment of the present invention is a compound represented byGeneral Formula (G1). In the case where a substituent represented byGeneral Formula (G1-1) is bonded to the benzene ring ofbenzo[b]naphtho[2,3-d]furan, the compound can have a higher tripletexcitation energy level (T₁ level) than in the case where thesubstituent is bonded to the naphthalene ring.

In General Formula (G1), one of R⁷ to R¹⁰ represents a substituentrepresented by General Formula (G1-1); R¹ to R⁶ and the others of R⁷ toR¹⁰ separately represent any one of hydrogen, an alkyl group having 1 to6 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, and anaryl group having 6 to 13 carbon atoms; A represents adibenzo[f,h]quinoxalinyl group; and Ar represents an arylene grouphaving 6 to 25 carbon atoms. The dibenzo[f,h]quinoxalinyl group, thearyl group, and the arylene group are separately unsubstituted orsubstituted by any one of an alkyl group having 1 to 6 carbon atoms, acycloalkyl group having 3 to 6 carbon atoms, and an aryl group having 6to 13 carbon atoms.

In particular, the substituent represented by General Formula (G1-1) ispreferably bonded to the 8-position of benzo[b]naphtho[2,3-d]furanskeleton in General Formula (G1) (that is, R¹⁰ in General Formula (G1)is preferably the substituent represented by General Formula (G1-1))because a high T₁ level can be achieved.

One embodiment of the present invention is a compound represented byGeneral Formula (G2).

In General Formula (G2), R¹ to R⁹ separately represent any one ofhydrogen, an alkyl group having 1 to 6 carbon atoms, a cycloalkyl grouphaving 3 to 6 carbon atoms, and an aryl group having 6 to 13 carbonatoms; A represents a dibenzo[f,h]quinoxalinyl group; and Ar representsan arylene group having 6 to 25 carbon atoms. Thedibenzo[f,h]quinoxalinyl group, the aryl group, and the arylene groupare separately unsubstituted or substituted by any one of an alkyl grouphaving 1 to 6 carbon atoms, a cycloalkyl group having 3 to 6 carbonatoms, and an aryl group having 6 to 13 carbon atoms.

In the compound represented by General Formula (G2), Ar is preferablybonded to the 2-position, the 6-position, or the 7-position of thedibenzo[f,h]quinoxaline skeleton for higher purity, a higher T₁ level,and the like. Preferably, Ar is bonded to the 2-position because thecompound can be more easily synthesized and thus can be provided atlower cost than in the case where Ar is bonded to the 6-position or the7-position. Preferably, Ar is bonded to the 6-position because a T₁level can be higher than in the case where Ar is bonded to the2-position or the 7-position. Preferably, Ar is bonded to the 7-positionbecause a T₁ level can be higher than in the case where Ar is bonded tothe 2-position. Preferably, Ar is bonded to the 6-position or the7-position because the solubility can often be higher and purificationand an increase in purity can be performed more easily than in the casewhere Ar is bonded to the 2-position.

One embodiment of the present invention is a compound represented byGeneral Formula (G3).

In General Formula (G3), R¹ to R⁹ and R¹¹ to R¹⁹ separately representany one of hydrogen, an alkyl group having 1 to 6 carbon atoms, acycloalkyl group having 3 to 6 carbon atoms, and an aryl group having 6to 13 carbon atoms, and Ar represents an arylene group having 6 to 25carbon atoms. The aryl group and the arylene group are separatelyunsubstituted or substituted by any one of an alkyl group having 1 to 6carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, and an arylgroup having 6 to 13 carbon atoms.

Specific examples of the structure of Ar in General Formulae (G1-1),(G2), and (G3) include substituents represented by Structural Formulae(1-1) to (1-18). Note that Ar may further have, as a substituent, anyone of an alkyl group having 1 to 4 carbon atoms, a cycloalkyl grouphaving 3 to 6 carbon atoms, and an aryl group having 6 to 13 carbonatoms. As examples of the aryl group having 6 to 13 carbon atoms, aphenyl group, a naphthyl group, and a fluorenyl group can be given.Specific examples of Ar having a substituent are illustrated byStructural Formulae (1-12), (1-13), (1-15), and (1-18). Note that Arhaving a substituent is not limited to these examples.

Preferably, Ar has one or more kinds of rings selected from a benzenering, a fluorene ring, and a naphthalene ring. Preferably, Ar is asubstituent including one or more kinds of rings selected from a benzenering, a fluorene ring, and a naphthalene ring, examples of which includea phenylene group, a biphenylene group, a terphenylene group, aquaterphenylene group, a naphthalene-diyl group, and a 9H-fluoren-diylgroup. In that case, the compound of one embodiment of the presentinvention can have high triplet excitation energy.

Specific examples of R¹ to R¹⁹ in General Formulae (G1) to (G3) includesubstituents represented by Structural Formulae (2-1) to (2-23). Notethat when R¹ to R¹⁹ represent aryl groups, R¹ to R¹⁹ may further have,as a substituent, any one of an alkyl group having 1 to 4 carbon atoms,a cycloalkyl group having 3 to 6 carbon atoms, and an aryl group having6 to 13 carbon atoms. As examples of the aryl group having 6 to 13carbon atoms, a phenyl group, a naphthyl group, and a fluorenyl groupcan be given. Specific examples of the aryl group having a substituentare illustrated by Structural Formulae (2-13) to (2-22). Note that R¹ toR¹⁹ each having a substituent are not limited to these examples.

Specific examples of the compound of one embodiment of the presentinvention include heterocyclic compounds represented by StructuralFormulae (100) to (155). However, the present invention is not limitedto these structural formulae.

A variety of reactions can be applied to a method for synthesizing thecompound of one embodiment of the present invention. As an example of amethod for synthesizing the compound represented by General Formula(G0), a method for synthesizing the compound represented by GeneralFormula (G1) in which R¹⁰ is the substituent represented by GeneralFormula (G1-1), i.e., a method for synthesizing the compound representedby General Formula (G2), is described below. Note that the methods forsynthesizing the compound of one embodiment of the present invention arenot limited to the synthesis methods below.

The compound represented by General Formula (G2) can be synthesizedunder Synthesis Scheme (A−1) below. That is, the compound represented byGeneral Formula (G2) can be obtained by coupling of abenzo[b]naphtho[2,3-d]furan compound (Compound 1) and adibenzo[f,h]quinoxaline compound (Compound 2).

In Synthesis Scheme (A−1), A represents a substituted or unsubstituteddibenzo[f,h]quinoxalinyl group; Ar represents a substituted orunsubstituted arylene group having 6 to 25 carbon atoms; X¹ and X²separately represent any one of a halogen, a trifluoromethanesulfonylgroup, a boronic acid group, an organoboron group, a magnesium halidegroup, an organotin group, and the like; and R¹ to R⁹ separatelyrepresent any one of hydrogen, an alkyl group having 1 to 6 carbonatoms, a cycloalkyl group having 3 to 6 carbon atoms, and a substitutedor unsubstituted aryl group having 6 to 13 carbon atoms.

When a Suzuki-Miyaura coupling reaction using a palladium catalyst isperformed under Synthesis Scheme (A−1), X¹ and X² separately representany one of a halogen, a boronic acid group, an organoboron group, and atrifluoromethanesulfonyl group. It is preferable that the halogen be anyone of iodine, bromine, and chlorine. In the reaction, a palladiumcompound such as bis(dibenzylideneacetone)palladium(0), palladium(II)acetate, [1,1′-bis(diphenylphosphino)ferrocene]palladium(II) dichloride,or tetrakis(triphenylphosphine)palladium(0) and a ligand such astri(tert-butyl)phosphine, tri(n-hexyl)phosphine, tricyclohexylphosphine,di(1-adamantyl)-n-butylphosphine,2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl, ortri(ortho-tolyl)phosphine can be used. In addition, in the reaction, anorganic base such as sodium tert-butoxide, an inorganic base such aspotassium carbonate, cesium carbonate, or sodium carbonate, or the likecan be used. Furthermore, in the reaction, toluene, xylene, benzene,tetrahydrofuran, dioxane, ethanol, methanol, water, or the like can beused as a solvent. The reagents that can be used in the reaction are notlimited thereto.

The reaction performed under Synthesis Scheme (A−1) is not limited to aSuzuki-Miyaura coupling reaction, and a Migita-Kosugi-Stille couplingreaction using an organotin compound, a Kumada-Tamao-Corriu couplingreaction using a Grignard reagent, a Negishi coupling reaction using anorganozinc compound, a reaction using copper or a copper compound, orthe like can also be employed.

By a method similar to the above, it is also possible to synthesize acompound in which the substituent represented by General Formula (G1-1)is bonded to any one of the 1- to 10-positions ofbenzo[b]naphtho[2,3-d]furan (i.e., a compound represented by GeneralFormula (G1) in which any one of R¹ to R¹⁰ is the substituentrepresented by General Formula (G1-1)).

Thus, the compound of this embodiment can be synthesized.

A compound in which a halogen (iodine, bromine, or chlorine), atrifluoromethanesulfonyl group, a boronic acid group, an organoborongroup, a magnesium halide group, an organotin group, or the like isbonded to the 8-position of benzo[b]naphtho[2,3-d]furan and which isused in synthesis of the compound of one embodiment of the presentinvention is also one embodiment of the present invention.

One embodiment of the present invention is a compound represented byGeneral Formula (G4).

In General Formula (G4), R¹ to R⁹ separately represent any one ofhydrogen, an alkyl group having 1 to 6 carbon atoms, a cycloalkyl grouphaving 3 to 6 carbon atoms, and an aryl group having 6 to 13 carbonatoms, and R¹⁰ represents any one of chlorine, bromine, boron, iodine, aboronic acid group, and an organoboron group. The aryl group isunsubstituted or substituted by any one of an alkyl group having 1 to 6carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, and an arylgroup having 6 to 13 carbon atoms.

<Synthesis Method of Compound Represented by General Formula (G4)>

A method for synthesizing the compound represented by General Formula(G4) is described. Note that the methods for synthesizing the compoundof one embodiment of the present invention represented by GeneralFormula (G4) are not limited to the synthesis methods below.

The compound represented by General Formula (G4) can be synthesizedunder Synthesis Schemes (X-1) and (X-2) below, for example.

First, as shown in Synthesis Scheme (X-1), Compound 3 is coupled withCompound 4, so that an alcohol (Compound 5) can be obtained.

In Synthesis Scheme (X-1), R¹ to R⁹ separately represent any one ofhydrogen, an alkyl group having 1 to 6 carbon atoms, a cycloalkyl grouphaving 3 to 6 carbon atoms, and an aryl group having 6 to 13 carbonatoms; R¹⁰ represents any one of chlorine, bromine, boron, iodine, aboronic acid group, and an organoboron group; and X¹ and X² separatelyrepresent any one of a halogen, a trifluoromethanesulfonyl group, aboronic acid group, an organoboron group, a magnesium halide group, anorganotin group, and the like.

In Synthesis Scheme (X-1), the hydroxyl group in Compound 4 may beprotected by an alkyl group or the like.

When a Suzuki-Miyaura coupling reaction using a palladium catalyst isperformed under Synthesis Scheme (X-1), X¹ and X² separately representany one of a halogen, a boronic acid group, an organoboron group, and atrifluoromethanesulfonyl group. It is preferable that the halogen be anyone of iodine, bromine, and chlorine. In the reaction, a palladiumcompound such as bis(dibenzylideneacetone)palladium(0), palladium(II)acetate, [1,1′-bis(diphenylphosphino)ferrocene]palladium(II) dichloride,or tetrakis(triphenylphosphine)palladium(0) and a ligand such astri(tert-butyl)phosphine, tri(n-hexyl)phosphine, tricyclohexylphosphine,di(1-adamantyl)-n-butylphosphine,2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl, ortri(ortho-tolyl)phosphine can be used. In addition, in the reaction, anorganic base such as sodium tert-butoxide, an inorganic base such aspotassium carbonate, cesium carbonate, or sodium carbonate, or the likecan be used. Furthermore, in the reaction, toluene, xylene, benzene,tetrahydrofuran, dioxane, ethanol, methanol, water, or the like can beused as a solvent. Reagents that can be used in the reaction are notlimited thereto.

The reaction performed under Synthesis Scheme (X-1) is not limited to aSuzuki-Miyaura coupling reaction, and a Migita-Kosugi-Stille couplingreaction using an organotin compound, a Kumada-Tamao-Corriu couplingreaction using a Grignard reagent, a Negishi coupling reaction using anorganozinc compound, a reaction using copper or a copper compound, orthe like can also be employed.

Then, as shown in Synthesis Scheme (X-2), an ether linkage is formed inthe alcohol (Compound 5) by the Williamson synthesis, so that abenzo[b]naphtho[2,3-d]furan derivative (Compound 6) can be synthesized.

In Synthesis Scheme (X-2), R¹ to R⁹ separately represent any one ofhydrogen, an alkyl group having 1 to 6 carbon atoms, a cycloalkyl grouphaving 3 to 6 carbon atoms, and an aryl group having 6 to 13 carbonatoms, and R¹⁰ represents any one of chlorine, bromine, boron, iodine, aboronic acid group, and an organoboron group.

In the case where the hydroxyl group in Compound 4 is protected by analkyl group or the like in Synthesis Scheme (X-1), protecting deblockingneeds to be performed using boron tribromide or the like beforeSynthesis Scheme (X-2) so that the protected hydroxyl group is returnedto a hydroxyl group.

In the case where the Williamson synthesis is performed in SynthesisScheme (X-2), a base such as potassium carbonate or sodium carbonate anda solvent such as N-methyl-2-pyrrolidone (NMP) can be used. Note thatthe base and the solvent which can be used are not limited thereto.

A method for synthesizing the compound of one embodiment of the presentinvention with the use of the compound (Compound 7) which is representedby General Formula (G4) and in which R¹⁰ represents chlorine isdescribed with reference to Synthesis Scheme (X-3).

In Synthesis Scheme (X-3), R¹ to R⁹ separately represent any one ofhydrogen, an alkyl group having 1 to 6 carbon atoms, a cycloalkyl grouphaving 3 to 6 carbon atoms, and an aryl group having 6 to 13 carbonatoms.

In Synthesis Scheme (X-3), an organolithium compound (Compound 8), whichis obtained by substitution of chlorine in the chlorine compound(Compound 7) with lithium, is used to perform substitution with aboronic acid group, substitution with bromine, or substitution withiodine, whereby a boronic acid compound (Compound 9), a bromine compound(Compound 10), or an iodine compound (Compound 11) can be synthesized.

Reagents that can be used for Synthesis Scheme (X-3) are as follows: anorganolithium reagent such as n-butyllithium or t-butyllithium in thesynthesis of the organolithium compound; trimethyl borate or the like inthe substitution with a boronic acid group; iodine or the like in thesubstitution with iodine; and bromine or the like in the substitutionwith bromine. The reagents that can be used are not limited thereto.

Next, a method for synthesizing the compound (Compound 12) which isrepresented by General Formula (G4) and in which R¹⁰ represents4,4,5,5-tetramethyl-1,3,2-dioxaborolane is described with reference toSynthesis Scheme (X-4).

In Synthesis Scheme (X-4), R¹ to R⁹ separately represent any one ofhydrogen, an alkyl group having 1 to 6 carbon atoms, a cycloalkyl grouphaving 3 to 6 carbon atoms, and an aryl group having 6 to 13 carbonatoms, and R¹⁰ represents any one of chlorine, bromine, and iodine.

As shown in Synthesis Scheme (X-4), Compound 6 that is a halogencompound is coupled with bis(pinacolato)diboron, so that an organoboroncompound (Compound 12) can be obtained. In Synthesis Scheme (X-4), apalladium compound such as bis(dibenzylideneacetone)palladium(0),palladium(II) acetate,[1,1′-bis(diphenylphosphino)ferrocene]palladium(II) dichloride, ortetrakis(triphenylphosphine)palladium(0) and a ligand such astri(tert-butyl)phosphine, tri(n-hexyl)phosphine, tricyclohexylphosphine,di(1-adamantyl)-n-butylphosphine,2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl, ortri(ortho-tolyl)phosphine can be used. In addition, in the reaction, anorganic base such as sodium tert-butoxide, an inorganic base such aspotassium carbonate, cesium carbonate, or sodium carbonate, or the likecan be used. Furthermore, in the reaction, toluene, xylene, benzene,tetrahydrofuran, dioxane, ethanol, methanol, water, or the like can beused as a solvent. Reagents that can be used in the reaction are notlimited thereto.

Specific examples of the compound of one embodiment of the presentinvention include compounds represented by Structural Formulae (201) to(215). However, the present invention is not limited to these structuralformulae.

In a light-emitting element, the compound of this embodiment can befavorably used as a host material of a light-emitting layer, in which alight-emitting substance is dispersed, or a material of anelectron-transport layer. By the use of the compound of this embodiment,a light-emitting element with a long lifetime can be provided.

This embodiment can be combined with any other embodiment asappropriate.

Embodiment 2

In this embodiment, light-emitting elements of embodiments of thepresent invention will be described with reference to FIGS. 1A to 1D.

A light-emitting element of one embodiment of the present invention hasa layer containing the compound described in Embodiment 1 between a pairof electrodes.

The compound included in the light-emitting element of one embodiment ofthe present invention is sterically bulky and highly resistant to heat.In addition, the compound has high film quality. Accordingly, the use ofthe compound enables a light-emitting element to have a long lifetime.

Furthermore, the compound can accept electrons and holes since thecompound has a dibenzo[f,h]quinoxaline skeleton as an electron-transportskeleton and a benzo[b]naphtho[2,3-d]furan skeleton as a hole-transportskeleton. Accordingly, by the use of the compound as a host material ofa light-emitting layer, electrons and holes recombine in thelight-emitting layer and it is possible to inhibit a reduction inlifetime of the light-emitting element. That is, a preferred embodimentof the present invention is a light-emitting element including, betweena pair of electrodes, a light-emitting layer containing a light-emittingsubstance (guest material) and the above compound serving as a hostmaterial in which the light-emitting substance is dispersed.

The light-emitting element of this embodiment includes a layer (ELlayer) containing a light-emitting organic compound between a pair ofelectrodes (a first electrode and a second electrode). One of the firstelectrode and the second electrode functions as an anode, and the otherfunctions as a cathode. In this embodiment, the EL layer contains thecompound of one embodiment of the present invention which is describedin Embodiment 1.

<<Structural Example of Light-Emitting Element>>

A light-emitting element illustrated in FIG. 1A includes an EL layer 203between a first electrode 201 and a second electrode 205. In thisembodiment, the first electrode 201 serves as an anode and the secondelectrode 205 serves as a cathode.

When a voltage higher than the threshold voltage of the light-emittingelement is applied between the first electrode 201 and the secondelectrode 205, holes are injected from the first electrode 201 side tothe EL layer 203 and electrons are injected from the second electrode205 side to the EL layer 203. The injected electrons and holes recombinein the EL layer 203 and a light-emitting substance contained in the ELlayer 203 emits light.

The EL layer 203 includes at least a light-emitting layer 303 containinga light-emitting substance.

Furthermore, when a plurality of light-emitting layers are provided inthe EL layer and emission colors of the layers are made different, lightemission of a desired color can be provided from the light-emittingelement as a whole. For example, the emission colors of first and secondlight-emitting layers are complementary in a light-emitting elementhaving the two light-emitting layers, so that the light-emitting elementcan be made to emit white light as a whole. Note that “complementarycolors” refer to colors that can produce an achromatic color when mixed.In other words, when light components obtained from substances that emitlight of complementary colors are mixed, white emission can be obtained.Furthermore, the same applies to a light-emitting element having threeor more light-emitting layers.

In addition to the light-emitting layer, the EL layer 203 may furtherinclude a layer containing a substance with a high hole-injectionproperty, a substance with a high hole-transport property, a substancewith a high electron-transport property, a substance with a highelectron-injection property, a substance with a bipolar property (asubstance with a high electron-transport property and a highhole-transport property), or the like. Either a low molecular compoundor a high molecular compound can be used for the EL layer 203, and aninorganic compound may be used.

A light-emitting element illustrated in FIG. 1B includes the EL layer203 between the first electrode 201 and the second electrode 205, and inthe EL layer 203, a hole-injection layer 301, a hole-transport layer302, the light-emitting layer 303, an electron-transport layer 304, andan electron-injection layer 305 are stacked in that order from the firstelectrode 201 side.

The compound of one embodiment of the present invention is preferablyused for the light-emitting layer 303 or the electron-transport layer304. In this embodiment, an example is described in which the compoundof one embodiment of the present invention is used as the host materialin the light-emitting layer 303.

As in light-emitting elements illustrated in FIGS. 1C and 1D, aplurality of EL layers may be stacked between the first electrode 201and the second electrode 205. In this case, an intermediate layer 207 ispreferably provided between the stacked EL layers. The intermediatelayer 207 includes at least a charge-generation region.

For example, the light-emitting element illustrated in FIG. 1C includesthe intermediate layer 207 between a first EL layer 203 a and a secondEL layer 203 b. The light-emitting element illustrated in FIG. 1Dincludes n EL layers (n is a natural number of 2 or more), and theintermediate layers 207 between the EL layers.

The behaviors of electrons and holes in the intermediate layer 207provided between the EL layer 203(m) and the EL layer 203(m+1) will bedescribed. When a voltage higher than the threshold voltage of thelight-emitting element is applied between the first electrode 201 andthe second electrode 205, holes and electrons are generated in theintermediate layer 207, and the holes move into the EL layer 203(m+1)provided on the second electrode 205 side and the electrons move intothe EL layer 203(m) provided on the first electrode 201 side. The holesinjected into the EL layer 203(m+1) recombine with electrons injectedfrom the second electrode 205 side, so that a light-emitting substancecontained in the EL layer 203(m+1) emits light. Furthermore, theelectrons injected into the EL layer 203(m) recombine with holesinjected from the first electrode 201 side, so that a light-emittingsubstance contained in the EL layer 203(m) emits light. Thus, the holesand electrons generated in the intermediate layer 207 cause lightemission in different EL layers.

Note that the EL layers can be provided in contact with each other withno intermediate layer interposed therebetween when these EL layers allowthe same structure as the intermediate layer to be formed therebetween.For example, when the charge-generation region is formed over onesurface of an EL layer, another EL layer can be provided in contact withthe surface.

Furthermore, when emission colors of the EL layers are made different,light emission of a desired color can be provided from thelight-emitting element as a whole. For example, the emission colors ofthe first and second EL layers are complementary in a light-emittingelement having the two EL layers, so that the light-emitting element canbe made to emit white light as a whole. The same applies to alight-emitting element having three or more EL layers.

<<Materials of Light-Emitting Element>>

Examples of materials which can be used for each layer will be givenbelow. Note that each layer is not limited to a single layer, and may bea stack including two or more layers.

<Anode>

The electrode serving as the anode (the first electrode 201 in thisembodiment) can be formed using one or more kinds of conductive metals,conductive alloys, conductive compounds, and the like. In particular, itis preferable to use a material with a high work function (4.0 eV ormore). The examples include indium tin oxide (ITO), indium tin oxidecontaining silicon or silicon oxide, indium zinc oxide, indium oxidecontaining tungsten oxide and zinc oxide, graphene, gold, platinum,nickel, tungsten, chromium, molybdenum, iron, cobalt, copper, palladium,titanium, and a nitride of a metal material (e.g., titanium nitride).

When the anode is in contact with the charge-generation region, any of avariety of conductive materials can be used regardless of their workfunctions; for example, aluminum, silver, an alloy containing aluminum,or the like can be used.

<Cathode>

The electrode serving as the cathode (the second electrode 205 in thisembodiment) can be formed using one or more kinds of conductive metals,conductive alloys, conductive compounds, and the like. In particular, itis preferable to use a material with a low work function (3.8 eV orless). The examples include aluminum, silver, an element belonging toGroup 1 or 2 of the periodic table (e.g., an alkali metal such aslithium or cesium, an alkaline earth metal such as calcium or strontium,or magnesium), an alloy containing any of these elements (e.g., Mg—Ag orAl—Li), a rare earth metal such as europium or ytterbium, and an alloycontaining any of these rare earth metals.

Note that when the cathode is in contact with the charge-generationregion, any of a variety of conductive materials can be used regardlessof its work function. For example, ITO or indium tin oxide containingsilicon or silicon oxide can be used.

The electrodes may be formed separately by a vacuum evaporation methodor a sputtering method. Alternatively, when a silver paste or the likeis used, a coating method or an inkjet method may be used.

<Light-Emitting Layer>

The light-emitting layer 303 contains a light-emitting substance. In anexample described in this embodiment, the light-emitting layer 303contains a guest material and a host material in which the guestmaterial is dispersed and the compound of one embodiment of the presentinvention is used as the host material. The compound of one embodimentof the present invention can be favorably used as a host material in alight-emitting layer when a light-emitting substance is a phosphorescentcompound emitting light in a wavelength range from red to green or afluorescent compound.

When the light-emitting layer has the structure in which the guestmaterial is dispersed in the host material, the crystallization of thelight-emitting layer can be inhibited. Furthermore, it is possible toinhibit concentration quenching due to high concentration of the guestmaterial; thus, the light-emitting element can have higher emissionefficiency.

In addition to the guest material and the host material, thelight-emitting layer may contain another compound. Furthermore, inaddition to the light-emitting layer containing the compound of oneembodiment of the present invention, the light-emitting element of oneembodiment of the present invention may include another light-emittinglayer. In that case, a fluorescent compound, a phosphorescent compound,or a substance emitting thermally activated delayed fluorescence can beused as the light-emitting substance, and a compound to be describedbelow which easily accepts electrons or a compound to be described belowwhich easily accepts holes can be used as the host material.

Note that it is preferable that the T₁ level of the host material (or amaterial other than the guest material in the light-emitting layer) behigher than the T₁ level of the guest material. This is because, whenthe T₁ level of the host material is lower than that of the guestmaterial, the triplet excitation energy of the guest material, which isto contribute to light emission, is quenched by the host material andaccordingly the emission efficiency is reduced.

Here, for improvement in efficiency of energy transfer from a hostmaterial to a guest material, Förster mechanism (dipole-dipoleinteraction) and Dexter mechanism (electron exchange interaction), whichare known as mechanisms of energy transfer between molecules, areconsidered. According to the mechanisms, it is preferable that anemission spectrum of a host material (fluorescence spectrum in energytransfer from a singlet excited state, phosphorescence spectrum inenergy transfer from a triplet excited state) have a large overlap withan absorption spectrum of a guest material (specifically, spectrum in anabsorption band on the longest wavelength (lowest energy) side).

However, in general, it is difficult to obtain an overlap between afluorescence spectrum of a host material and an absorption spectrum inan absorption band on the longest wavelength (lowest energy) side of aguest material. The reason for this is as follows: if the fluorescencespectrum of the host material overlaps with the absorption spectrum inthe absorption band on the longest wavelength (lowest energy) side ofthe guest material, because the phosphorescence spectrum of the hostmaterial is located on the longer wavelength (lower energy) side thanthe fluorescence spectrum, the T₁ level of the host material becomeslower than the T₁ level of the phosphorescent compound and theabove-described problem of quenching occurs; yet, when the host materialis designed in such a manner that the T₁ level of the host material ishigher than the T₁ level of the phosphorescent compound to avoid theproblem of quenching, the fluorescence spectrum of the host material isshifted to the shorter wavelength (higher energy) side, and thus thefluorescence spectrum does not have any overlap with the absorptionspectrum in the absorption band on the longest wavelength (lowestenergy) side of the guest material. For this reason, in general, it isdifficult to obtain an overlap between a fluorescence spectrum of a hostmaterial and an absorption spectrum in an absorption band on the longestwavelength (lowest energy) side of a guest material so as to maximizeenergy transfer from a singlet excited state of a host material.

Thus, it is preferable that in a light-emitting layer of alight-emitting element which uses a phosphorescent compound as a guestmaterial, a third substance be contained in addition to thephosphorescent compound and the host material (which are respectivelyregarded as a first substance and a second substance contained in thelight-emitting layer), and the host material forms an exciplex (alsoreferred to as excited complex) in combination with the third substance.In that case, the host material and the third substance form an exciplexat the time of recombination of carriers (electrons and holes) in thelight-emitting layer. Thus, in the light-emitting layer, fluorescencespectra of the host material and the third substance are converted intoan emission spectrum of the exciplex which is located on a longerwavelength side. Moreover, when the host material and the thirdsubstance are selected such that the emission spectrum of the exciplexhas a large overlap with the absorption spectrum of the guest material,energy transfer from a singlet excited state can be maximized. Note thatalso in the case of a triplet excited state, energy transfer from theexciplex, not the host material, is considered to occur. In oneembodiment of the present invention to which such a structure isapplied, energy transfer efficiency can be improved owing to energytransfer utilizing an overlap between an emission spectrum of anexciplex and an absorption spectrum of a phosphorescent compound;accordingly, a light-emitting element with high external quantumefficiency can be provided.

As the guest material, a phosphorescent compound to be described belowcan be used. Although any combination of the host material and the thirdsubstance can be used as long as an exciplex is formed, a compound whicheasily accepts electrons (a compound having an electron-trappingproperty) and a compound which easily accepts holes (a compound having ahole-trapping property) are preferably combined. The compound of oneembodiment of the present invention can be used as a compound having anelectron-trapping property.

Thus, the light-emitting element of one embodiment of the presentinvention includes, between a pair of electrodes, a light-emitting layercontaining a phosphorescent compound emitting light in a wavelengthrange from red to green, the compound of one embodiment of the presentinvention, and a compound which easily accepts holes.

Examples of a compound which easily accepts holes and which can be usedas the host material or the third substance are a π-electron richheteroaromatic compound (e.g., a carbazole derivative or an indolederivative) and an aromatic amine compound.

Specifically, the following examples can be given:N-(1,1′-biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9H-fluoren-2-amine(abbreviation: PCBBiF),4-phenyl-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation:PCBAlBP),4,4′-di(1-naphthyl)-4″-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBNBB),3-[N-(1-naphthyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole(abbreviation: PCzPCN1),4,4′,4″-tris[N-(1-naphthyl)-N-phenylamino]triphenylamine (abbreviation:1′-TNATA),2,7-bis[N-(4-diphenylaminophenyl)-N-phenylamino]spiro-9,9′-bifluorene(abbreviation: DPA2 SF),N,N′-bis(9-phenylcarbazol-3-yl)-N,N′-diphenylbenzene-1,3-diamine(abbreviation: PCA2B),N-(9,9-dimethyl-2-diphenylamino-9H-fluoren-7-yl)diphenylamine(abbreviation: DPNF),N,N′,N″-triphenyl-N,N′,N″-tris(9-phenylcarbazol-3-yl)benzene-1,3,5-triamine(abbreviation: PCA3B),2-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]spiro-9,9′-bifluorene(abbreviation: PCASF),2-[N-(4-diphenylaminophenyl)-N-phenylamino]spiro-9,9′-bifluorene(abbreviation: DPASF),N,N′-bis[4-(carbazol-9-yl)phenyl]-N,N′-diphenyl-9,9-dimethylfluorene-2,7-diamine(abbreviation: YGA2F),N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine(abbreviation: TPD),4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (abbreviation:DPAB),N-(9,9-dimethyl-9H-fluoren-2-yl)-N-{9,9-dimethyl-2-[N-phenyl-N-(9,9-dimethyl-9H-fluoren-2-yl)amino]-9H-fluoren-7-yl}phenylamine(abbreviation: DFLADFL),3-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA1),3,6-bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA2),3-[N-(4-diphenylaminophenyl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzDPA1),3,6-bis[N-(4-diphenylaminophenyl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzDPA2),4,4′-bis(N-{4-[N-(3-methylphenyl)-N-phenylamino]phenyl}-N-phenylamino)biphenyl(abbreviation: DNTPD), and3,6-bis[N-(4-diphenylaminophenyl)-N-(1-naphthyl)amino]-9-phenylcarbazole(abbreviation: PCzTPN2).

The following examples can also be given: aromatic amine compounds suchas 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB orα-NPD), 4,4′,4″-tris(N,N-diphenylamino)triphenylamine (abbreviation:TDATA), 4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine(abbreviation: MTDATA),4,4′-bis[N-(spiro-9,9′-bifluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: BSPB), 4,4′,4″-tris(N-carbazolyl)triphenylamine(abbreviation: TCTA), 4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine(abbreviation: BPAFLP), and4,4′-bis[N-(9,9-dimethylfluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: DFLDPBi); and carbazole derivatives such as4,4′-di(N-carbazolyl)biphenyl (abbreviation: CBP),9-[4-(10-phenyl-9-anthracenyl)phenyl]-9H-carbazole (abbreviation: CzPA),and 9-phenyl-3-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole(abbreviation: PCzPA). In addition, high molecular compounds such aspoly(N-vinylcarbazole) (abbreviation: PVK), poly(4-vinyltriphenylamine)(abbreviation: PVTPA),poly[N-(4-{N′-[4-(4-diphenylamino)phenyl]phenyl-N′-phenylamino}phenyl)methacrylamide](abbreviation: PTPDMA), andpoly[N,N-bis(4-butylphenyl)-N,N-bis(phenyl)benzidine] (abbreviation:Poly-TPD) can be given.

Examples of the compound which easily accepts electrons and which can beused as the host material or the third substance include the compound ofone embodiment of the present invention, a π-electron deficientheteroaromatic compound such as a nitrogen-containing heteroaromaticcompound, a metal complex having a quinoline skeleton or abenzoquinoline skeleton, and a metal complex having an oxazole-basedligand or a thiazole-based ligand.

Specific examples include the following: metal complexes such asbis(10-hydroxybenzo[h]quinolinato)beryllium (abbreviation: BeBq₂),bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum (abbreviation:BAlq), bis(8-quinolinolato)zinc (II) (abbreviation: Znq),bis[2-(2-hydroxyphenyl)benzoxazolato]zinc (abbreviation: Zn(BOX)₂), andbis[2-(2-hydroxyphenyl)benzothiazolato]zinc (abbreviation: Zn(BTZ)₂);heterocyclic compounds having polyazole skeletons, such as2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation:PBD), 3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole(abbreviation: TAZ),1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene(abbreviation: OXD-7),9-[4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl]-9H-carbazole (abbreviation:CO11), 2,2′,2″-(1,3,5-benzenetriyl)tris(1-phenyl-1H-benzimidazole)(abbreviation: TPBI), and2-[3-(dibenzothiophen-4-yl)phenyl]-1-phenyl-1H-benzimidazole(abbreviation: mDBTBIm-II); heterocyclic compounds having quinoxalineskeletons or dibenzoquinoxaline skeletons, such as2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:2mDBTPDBq-II),2-[3′-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline(abbreviation: 2mDBTBPDBq-II),2-[4-(3,6-diphenyl-9H-carbazol-9-yl)phenyl]dibenzo[f,h]quinoxaline(abbreviation: 2CzPDBq-III), 7-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 7mDBTPDBq-II),6-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:6mDBTPDBq-II), and2-[3′-(9H-carbazol-9-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline(abbreviation: 2mCzBPDBq); heterocyclic compounds having diazineskeletons (pyrimidine skeletons or pyrazine skeletons), such as4,6-bis[3-(phenanthren-9-yl)phenyl]pyrimidine (abbreviation:4,6mPnP2Pm), 4,6-bis[3-(9H-carbazol-9-yl)phenyl]pyrimidine(abbreviation: 4,6mCzP2Pm), and4,6-bis[3-(4-dibenzothienyl)phenyl]pyrimidine (abbreviation:4,6mDBTP2Pm-II); and heterocyclic compounds having pyridine skeletons,such as 3,5-bis[3-(9H-carbazol-9-yl)phenyl]pyridine (abbreviation: 3,5DCzPPy), 1,3,5-tri[3-(3-pyridyl)phenyl]benzene (abbreviation: TmPyPB),and 3,3′,5,5′-tetra[(m-pyridyl)-phen-3-yl]biphenyl (abbreviation:BP4mPy). Among the above materials, heterocyclic compounds havingquinoxaline skeletons or dibenzoquinoxaline skeletons, heterocycliccompounds having diazine skeletons, and heterocyclic compounds havingpyridine skeletons are preferable because of their high reliability.

The following examples can also be given: metal complexes havingquinoline skeletons or benzoquinoline skeletons, such astris(8-quinolinolato)aluminum (abbreviation: Alq) andtris(4-methyl-8-quinolinolato)aluminum (abbreviation: Almq₃); andheteroaromatic compounds such as bathophenanthroline (abbreviation:BPhen), bathocuproine (abbreviation: BCP),3-(4-tert-butylphenyl)-4-(4-ethylphenyl)-5-(4-biphenylyl)-1,2,4-triazole(abbreviation: p-EtTAZ), and 4,4′-bis(5-methylbenzoxazol-2-yl)stilbene(abbreviation: BzOs). In addition, high molecular compounds such aspoly(2,5-pyridinediyl) (abbreviation: PPy),poly[(9,9-dihexylfluorene-2,7-diyl)-co-(pyridine-3,5-diyl)](abbreviation: PF-Py), andpoly[(9,9-dioctylfluorene-2,7-diyl)-co-(2,2′-bipyridine-6,6′-diyl)](abbreviation: PF-BPy) can be given.

The materials which can be used as the host material or the thirdsubstance are not limited to the above materials as long as the materialused as the host material forms an exciplex in combination with thematerial used as the third substance, an emission spectrum of theexciplex overlaps with an absorption spectrum of the guest material, anda peak of the emission spectrum of the exciplex is located on a longerwavelength side than a peak of the absorption spectrum of the guestmaterial.

Note that when a compound which easily accepts electrons and a compoundwhich easily accepts holes are used for the host material and the thirdsubstance, carrier balance can be controlled by the mixture ratio of thecompounds. Specifically, the ratio of the host material to the thirdsubstance is preferably from 1:9 to 9:1.

Furthermore, the exciplex may be formed at the interface between twolayers. For example, when a layer containing the compound which easilyaccepts electrons and a layer containing the compound which easilyaccepts holes are stacked, the exciplex is formed in the vicinity of theinterface thereof. These two layers may be used as the light-emittinglayer in the light-emitting element of one embodiment of the presentinvention. In that case, the phosphorescent compound may be added to thevicinity of the interface. The phosphorescent compound may be added toone of the two layers or both.

<<Guest Material>>

Examples of fluorescent compounds that can be used for thelight-emitting layer 303 are given. Examples of materials that emit bluelight are as follows:N,N′-bis(3-methylphenyl)-N,N′-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]pyrene-1,6-diamine(abbreviation: 1,6mMemFLPAPrn),N,N′-bis(dibenzofuran-4-yl)-N,N-diphenylpyrene-1,6-diamine(abbreviation: 1,6FrAPrn-II),N,N-bis[4-(9H-carbazol-9-yl)phenyl]-N,N′-diphenylstilbene-4,4′-diamine(abbreviation: YGA2S),4-(9H-carbazol-9-yl)-4′-(10-phenyl-9-anthryl)triphenylamine(abbreviation: YGAPA), and4-(10-phenyl-9-anthryl)-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBAPA). Examples of materials that emit green light areas follows: N-(9,10-diphenyl-2-anthryl)-N,9-diphenyl-9H-carbazol-3-amine(abbreviation: 2PCAPA),N-[9,10-bis(1,1′-biphenyl-2-yl)-2-anthryl]-N,9-diphenyl-9H-carbazol-3-amine(abbreviation: 2PCABPhA),N-(9,10-diphenyl-2-anthryl)-N,N′,N′-triphenyl-1,4-phenylenediamine(abbreviation: 2DPAPA),N-[9,10-bis(1,1′-biphenyl-2-yl)-2-anthryl]-N,N′,N′-triphenyl-1,4-phenylenediamine(abbreviation: 2DPABPhA),9,10-bis(1,1′-biphenyl-2-yl)-N-[4-(9H-carbazol-9-yl)phenyl]-N-phenylanthracen-2-amine(abbreviation: 2YGABPhA), and N,N,9-triphenylanthracen-9-amine(abbreviation: DPhAPhA). Examples of materials that emit yellow lightare as follows: rubrene and5,12-bis(1,1′-biphenyl-4-yl)-6,11-diphenyltetracene (abbreviation: BPT).Examples of materials that emit red light are as follows:N,N,N′,N′-tetrakis(4-methylphenyl)tetracene-5,11-diamine (abbreviation:p-mPhTD) and7,14-diphenyl-N,N,N′,N′-tetrakis(4-methylphenyl)acenaphtho[1,2-α]fluoranthene-3,10-diamine(abbreviation: p-mPhAFD).

Examples of phosphorescent compounds that can be used for thelight-emitting layer 303 are given. For example, a phosphorescentcompound having an emission peak at 440 nm to 520 nm is given, examplesof which include organometallic iridium complexes having 4H-triazoleskeletons, such as tris{2-[5-(2-methylphenyl)-4-(2,6-dimethylphenyl)-4H-1,2,4-triazol-3-yl-κN2]phenyl-KC}iridium(III) (abbreviation: [Ir(mpptz-dmp)₃]),tris(5-methyl-3,4-diphenyl-4H-1,2,4-triazolato)iridium(III)(abbreviation: [Ir(Mptz)₃]), andtris[4-(3-biphenyl)-5-isopropyl-3-phenyl-4H-1,2,4-triazolato]iridium(III) (abbreviation: [Ir(iPrptz-3b)₃]); organometallic iridiumcomplexes having 1H-triazole skeletons, such astris[3-methyl-1-(2-methylphenyl)-5-phenyl-1H-1,2,4-triazolato]iridium(III)(abbreviation: [Ir(Mptz1-mp)₃]) andtris(1-methyl-5-phenyl-3-propyl-1H-1,2,4-triazolato)iridium(III)(abbreviation: [Ir(Prptzl-Me)₃]); organometallic iridium complexeshaving imidazole skeletons, such asfac-tris[1-(2,6-diisopropylphenyl)-2-phenyl-1H-imidazole] iridium(III)(abbreviation: [Ir(iPrpmi)₃]) andtris[3-(2,6-dimethylphenyl)-7-methylimidazo[1,2-f]phenanthridinato]iridium(III)(abbreviation: [Ir(dmpimpt-Me)₃]); and organometallic iridium complexesin which a phenylpyridine derivative having an electron-withdrawinggroup is a ligand, such asbis[2-(4′,6′-difluorophenyl)pyridinato-N,C^(2′)]iridium(III)tetrakis(1-pyrazolyl)borate (abbreviation: FIr6),bis[2-(4′,6′-difluorophenyl)pyridinato-N,C^(2′)] iridium(III) picolinate(abbreviation: FIrpic),bis{2-[3′,5′-bis(trifluoromethyl)phenyl]pyridinato-N,C^(2′)}iridium(III)picolinate (abbreviation: [Ir(CF3ppy)₂(pic)]), andbis[2-(4′,6′-difluorophenyl)pyridinato-N,C^(2′)]iridium(III)acetylacetonate (abbreviation: FIr(acac)). Among the materials givenabove, the organometallic iridium complexes having 4H-triazole skeletonshave high reliability and high emission efficiency and are thusespecially preferable.

Examples of the phosphorescent compound having an emission peak at 520nm to 600 nm include organometallic iridium complexes having pyrimidineskeletons, such as tris(4-methyl-6-phenylpyrimidinato)iridium(III)(abbreviation: [Ir(mppm)₃]),tris(4-t-butyl-6-phenylpyrimidinato)iridium(III) (abbreviation:[Ir(tBuppm)₃]),(acetylacetonato)bis(6-methyl-4-phenylpyrimidinato)iridium(III)(abbreviation: [Ir(mppm)₂(acac)]),(acetylacetonato)bis(6-tert-butyl-4-phenylpyrimidinato)iridium(III)(abbreviation: [Ir(tBuppm)₂(acac)]),(acetylacetonato)bis[4-(2-norbornyl)-6-phenylpyrimidinato]iridium(III)(endo- and exo-mixture) (abbreviation: [Ir(nbppm)₂(acac)]),(acetylacetonato)bis[5-methyl-6-(2-methylphenyl)-4-phenylpyrimidinato]iridium(III)(abbreviation: [Ir(mpmppm)₂(acac)]), and(acetylacetonato)bis(4,6-diphenylpyrimidinato)iridium(III)(abbreviation: [Ir(dppm)₂(acac)]); organometallic iridium complexeshaving pyrazine skeletons, such as(acetylacetonato)bis(3,5-dimethyl-2-phenylpyrazinato)iridium(III)(abbreviation: [Ir(mppr-Me)₂(acac)]) and(acetylacetonato)bis(5-isopropyl-3-methyl-2-phenylpyrazinato)iridium(III)(abbreviation: [Ir(mppr-iPr)₂(acac)]); organometallic iridium complexeshaving pyridine skeletons, such astris(2-phenylpyridinato-N,C^(2′))iridium(III) (abbreviation:[Ir(ppy)₃]), bis(2-phenylpyridinato-N,C^(2′))iridium(III)acetylacetonate (abbreviation: [Ir(ppy)₂(acac)]),bis(benzo[h]quinolinato)iridium(III) acetylacetonate (abbreviation:[Ir(bzq)₂(acac)]), tris(benzo[h]quinolinato)iridium (III) (abbreviation:[Ir(bzq)₃]), tris(2-phenylquinolinato-N,C^(2′))iridium(III)(abbreviation: [Ir(pq)₃]), andbis(2-phenylquinolinato-N,C^(2′))iridium(III) acetylacetonate(abbreviation: [Ir(pq)₂(acac)]); and a rare earth metal complex such astris(acetylacetonato)(monophenanthroline)terbium(III) (abbreviation:[Tb(acac)₃(Phen)]). Among the above materials, the organometalliciridium complexes having pyrimidine skeletons are particularlypreferable because of their distinctively high reliability and emissionefficiency.

Examples of the phosphorescent compound having an emission peak at 600nm to 700 nm include organometallic iridium complexes having pyrimidineskeletons, such as(diisobutyrylmethanato)bis[4,6-bis(3-methylphenyl)pyrimidinato]iridium(III)(abbreviation: [Ir(5mdppm)₂(dibm)]),bis[4,6-bis(3-methylphenyl)pyrimidinato](dipivaloylmethanato)iridium(III)(abbreviation: [Ir(5mdppm)₂(dpm)]), andbis[4,6-di(naphthalen-1-yl)pyrimidinato](dipivaloylmethanato)iridium(III)(abbreviation: [Ir(dlnpm)₂(dpm)]); organometallic iridium complexeshaving pyrazine skeletons, such as(acetylacetonato)bis(2,3,5-triphenylpyrazinato)iridium(III)(abbreviation: [Ir(tppr)₂(acac)]),bis(2,3,5-triphenylpyrazinato)(dipivaloylmethanato)iridium(III)(abbreviation: [Ir(tppr)₂(dpm)]), and(acetylacetonato)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III)(abbreviation: [Ir(Fdpq)₂(acac)]); organometallic iridium complexeshaving pyridine skeletons, such astris(1-phenylisoquinolinato-N,C^(2′))iridium(III) (abbreviation:[Ir(piq)₃]) and bis(1-phenylisoquinolinato-N,C^(2′))iridium(III)acetylacetonate (abbreviation: [Ir(piq)₂(acac)]); a platinum complexsuch as 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin platinum(II)(abbreviation: PtOEP); and rare earth metal complexes such astris(1,3-diphenyl-1,3-propanedionato)(monophenanthroline)europium(III)(abbreviation: [Eu(DBM)₃(Phen)]) andtris[1-(2-thenoyl)-3,3,3-trifluoroacetonato](monophenanthroline)europium(III)(abbreviation: [Eu(TTA)₃(Phen)]). Among the materials given above, theorganometallic iridium complexes having pyrimidine skeletons havedistinctively high reliability and emission efficiency and are thusespecially preferable. Furthermore, the organometallic iridium complexeshaving pyrazine skeletons can provide red light emission with favorablechromaticity.

Alternatively, a high molecular compound can be used for thelight-emitting layer 303. Examples of the materials that emit blue lightinclude poly(9,9-dioctylfluorene-2,7-diyl) (abbreviation: POF),poly[(9,9-dioctylfluorene-2,7-diyl)-co-(2,5-dimethoxybenzene-1,4-diyl)](abbreviation: PF-DMOP), andpoly{(9,9-dioctylfluorene-2,7-diyl)-co-[N,N′-di-(p-butylphenyl)-1,4-diaminobenzene]}(abbreviation: TAB-PFH). Examples of the materials that emit green lightinclude poly(p-phenylenevinylene) (abbreviation: PPV),poly[(9,9-dihexylfluorene-2,7-diyl)-alt-co-(benzo[2,1,3]thiadiazole-4,7-diyl)](abbreviation: PFBT), andpoly[(9,9-dioctyl-2,7-divinylenefluorenylene)-alt-co-(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene)].Examples of the materials that emit orange to red light includepoly[2-methoxy-5-(2-ethylhexoxy)-1,4-phenylenevinylene] (abbreviation:MEH-PPV), poly(3-butylthiophene-2,5-diyl),poly{[9,9-dihexyl-2,7-bis(1-cyanovinylene)fluorenylene]-alt-co-[2,5-bis(N,N′-diphenylamino)-1,4-phenylene]}, andpoly{[2-methoxy-5-(2-ethylhexyloxy)-1,4-bis(1-cyanovinylenephenylene)]-alt-co-[2,5-bis(N,N′-diphenylamino)-1,4-phenylene]}(abbreviation: CN-PPV-DPD).

<Hole-Transport Layer>

The hole-transport layer 302 contains a substance with a highhole-transport property.

The substance with a high hole-transport property is a substance havinga hole-transport property higher than an electron-transport property,and is especially preferably a substance with a hole mobility of 10⁻⁶cm²/Vs or more.

For the hole-transport layer 302, it is possible to use any of thecompounds which easily accept holes and are described as examples of thesubstance applicable to the light-emitting layer 303.

It is also possible to use an aromatic hydrocarbon compound such as2-tert-butyl-9,10-di(2-naphthyl)anthracene (abbreviation: t-BuDNA),9,10-di(2-naphthyl)anthracene (abbreviation: DNA), or9,10-diphenylanthracene (abbreviation: DPAnth).

<Electron-Transport Layer>

The electron-transport layer 304 contains a substance with a highelectron-transport property.

The substance with a high electron-transport property is an organiccompound having an electron-transport property higher than ahole-transport property, and is especially preferably a substance withan electron mobility of 10⁻⁶ cm²/Vs or more.

For the electron-transport layer 304, it is possible to use any of thecompounds which easily accept electrons and are described as examples ofthe substance applicable to the light-emitting layer 303.

<Hole-Injection Layer>

The hole-injection layer 301 contains a substance with a highhole-injection property.

Examples of the substance with a high hole-injection property includemetal oxides such as molybdenum oxide, titanium oxide, vanadium oxide,rhenium oxide, ruthenium oxide, chromium oxide, zirconium oxide, hafniumoxide, tantalum oxide, silver oxide, tungsten oxide, and manganeseoxide.

Alternatively, it is possible to use a phthalocyanine-based compoundsuch as phthalocyanine (abbreviation: H2Pc) or copper(II) phthalocyanine(abbreviation: CuPc).

Further alternatively, it is possible to use an aromatic amine compoundwhich is a low molecular organic compound, such as TDATA, MTDATA, DPAB,DNTPD, 1,3,5-tris[N-(4-diphenylaminophenyl)-N-phenylamino]benzene(abbreviation: DPA3B), PCzPCA1, PCzPCA2, or PCzPCN1.

Further alternatively, it is possible to use a high molecular compoundsuch as PVK, PVTPA, PTPDMA, or Poly-TPD, or a high molecular compound towhich acid is added, such aspoly(3,4-ethylenedioxythiophene)/poly(styrenesulfonic acid) (PEDOT/PSS)or polyaniline/poly(styrenesulfonic acid) (PAni/PSS).

The hole-injection layer 301 may serve as the charge-generation region.When the hole-injection layer 301 in contact with the anode serves asthe charge-generation region, any of a variety of conductive materialscan be used for the anode regardless of their work functions. Materialscontained in the charge-generation region will be described later.

<Electron-Injection Layer>

The electron-injection layer 305 contains a substance with a highelectron-injection property.

Examples of the substance with a high electron-injection propertyinclude an alkali metal, an alkaline earth metal, a rare earth metal,and a compound thereof (e.g., an oxide thereof, a carbonate thereof, anda halide thereof), such as lithium, cesium, calcium, lithium oxide,lithium carbonate, cesium carbonate, lithium fluoride, cesium fluoride,calcium fluoride, and erbium fluoride. Electride can also be used. As anexample of electride, a substance in which electrons are added at highconcentration to an oxide containing calcium and aluminum can be given.

The electron-injection layer 305 may serve as the charge-generationregion. When the electron-injection layer 305 in contact with thecathode serves as the charge-generation region, any of a variety ofconductive materials can be used for the cathode regardless of theirwork functions. Materials contained in the charge-generation region willbe described later.

<Charge-Generation Region>

The charge-generation region may have either a structure in which anelectron acceptor (acceptor) is added to an organic compound with a highhole-transport property or a structure in which an electron donor(donor) is added to an organic compound with a high electron-transportproperty. Alternatively, these structures may be stacked.

As examples of an organic compound with a high hole-transport property,the above materials which can be used for the hole-transport layer canbe given, and as examples of an organic compound with a highelectron-transport property, the above materials which can be used forthe electron-transport layer can be given.

Furthermore, as the electron acceptor,7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation:F4-TCNQ), chloranil, and the like can be given. In addition, atransition metal oxide can be given. In addition, an oxide of metalsthat belong to Group 4 to Group 8 of the periodic table can be given.Specifically, vanadium oxide, niobium oxide, tantalum oxide, chromiumoxide, molybdenum oxide, tungsten oxide, manganese oxide, and rheniumoxide are preferable because of their high electron-acceptingproperties. Among these, molybdenum oxide is especially preferable sinceit is stable in the air, has a low hygroscopic property, and is easy tohandle.

Furthermore, as the electron donor, it is possible to use an alkalimetal, an alkaline earth metal, a rare earth metal, a metal belonging toGroup 2 or Group 13 of the periodic table, or an oxide or a carbonatethereof. Specifically, lithium, cesium, magnesium, calcium, ytterbium,indium, lithium oxide, cesium carbonate, or the like is preferably used.Alternatively, an organic compound such as tetrathianaphthacene may beused as the electron donor.

The above-described layers included in the EL layer 203 and theintermediate layer 207 can be formed separately by any of the followingmethods: an evaporation method (including a vacuum evaporation method),a transfer method, a printing method, an inkjet method, a coatingmethod, and the like.

This embodiment can be freely combined with any of other embodiments.

Embodiment 3

In this embodiment, light-emitting devices of embodiments of the presentinvention will be described with reference to FIGS. 2A and 2B and FIGS.3A to 3C.

Light-emitting devices including the light-emitting element of oneembodiment of the present invention are described in this embodiment asexamples. Since the light-emitting element has a long lifetime,light-emitting devices having high reliability can be provided.

Note that one embodiment of the present invention is not limited tothese examples, and the light-emitting element of one embodiment of thepresent invention and the compound of one embodiment of the presentinvention are not necessarily included.

FIG. 2A is a plan view of a light-emitting device of one embodiment ofthe present invention, and FIG. 2B is a cross-sectional view taken alongdashed-dotted line A-B in FIG. 2A.

In the light-emitting device of this embodiment, a light-emittingelement 403 is provided in a space 415 surrounded by a support substrate401, a sealing substrate 405, and a sealing material 407. Thelight-emitting element 403 is an organic EL element having abottom-emission structure; specifically, a first electrode 421 whichtransmits visible light is provided over the support substrate 401, anEL layer 423 is provided over the first electrode 421, and a secondelectrode 425 which reflects visible light is provided over the EL layer423. The EL layer 423 contains the compound of one embodiment of thepresent invention which is described in Embodiment 1.

A first terminal 409 a is electrically connected to an auxiliary wiring417 and the first electrode 421. An insulating layer 419 is providedover the first electrode 421 in a region which overlaps with theauxiliary wiring 417. The first terminal 409 a is electrically insulatedfrom the second electrode 425 by the insulating layer 419. A secondterminal 409 b is electrically connected to the second electrode 425.Note that although the first electrode 421 is formed over the auxiliarywiring 417 in this embodiment, the auxiliary wiring 417 may be formedover the first electrode 421.

A light extraction structure 411 a is preferably provided at theinterface between the support substrate 401 and the atmosphere. Whenprovided at the interface between the support substrate 401 and theatmosphere, the light extraction structure 411 a can reduce light thatcannot be extracted to the atmosphere because of total reflection,resulting in an increase in the light extraction efficiency of thelight-emitting device.

In addition, a light extraction structure 411 b is preferably providedat the interface between the light-emitting element 403 and the supportsubstrate 401. When the light extraction structure 411 b has unevenness,a planarization layer 413 is preferably provided between the lightextraction structure 411 b and the first electrode 421. Accordingly, thefirst electrode 421 can be a flat film, and generation of leakagecurrent in the EL layer 423 due to the unevenness of the first electrode421 can be prevented. Furthermore, because of the light extractionstructure 411 b at the interface between the planarization layer 413 andthe support substrate 401, light that cannot be extracted to theatmosphere because of total reflection can be reduced, so that the lightextraction efficiency of the light-emitting device can be increased.

As a material of the light extraction structure 411 a and the lightextraction structure 411 b, a resin can be used, for example.Alternatively, for the light extraction structure 411 a and the lightextraction structure 411 b, a hemispherical lens, a micro lens array, afilm provided with an uneven structure, a light diffusing film, or thelike can be used. For example, the light extraction structure 411 a andthe light extraction structure 411 b can be formed by attaching the lensor film to the support substrate 401 with an adhesive or the like whichhas substantially the same refractive index as the support substrate 401or the lens or film.

The surface of the planarization layer 413 which is in contact with thefirst electrode 421 is flatter than the surface of the planarizationlayer 413 which is in contact with the light extraction structure 411 b.As a material of the planarization layer 413, glass, liquid, a resin, orthe like having a light-transmitting property and a high refractiveindex can be used.

FIG. 3A is a plan view of a light-emitting device of one embodiment ofthe present invention, FIG. 3B is a cross-sectional view taken alongdashed-dotted line C-D in FIG. 3A, and FIG. 3C is a cross-sectional viewillustrating a modified example of the light-emitting portion.

An active matrix light-emitting device of this embodiment includes, overa support substrate 501, a light-emitting portion 551 (the cross sectionof which is illustrated in FIG. 3B and FIG. 3C as a light-emittingportion 551 a and a light-emitting portion 551 b, respectively), adriver circuit portion 552 (gate side driver circuit portion), a drivercircuit portion 553 (source side driver circuit portion), and a sealingmaterial 507. The light-emitting portion 551 and the driver circuitportions 552 and 553 are sealed in a space 515 surrounded by the supportsubstrate 501, a sealing substrate 505, and the sealing material 507.

Any of a separate coloring method, a color filter method, and a colorconversion method can be applied to the light-emitting device of oneembodiment of the present invention. The light-emitting portion 551 afabricated by a color filter method is illustrated in FIG. 3B, and thelight-emitting portion 551 b fabricated by a separate coloring method isillustrated in FIG. 3C.

Each of the light-emitting portion 551 a and the light-emitting portion551 b includes a plurality of light-emitting units each including aswitching transistor 541 a, a current control transistor 541 b, and asecond electrode 525 electrically connected to a wiring (a sourceelectrode or a drain electrode) of the current control transistor 541 b.

A light-emitting element 503 included in the light-emitting portion 551a has a bottom-emission structure and includes a first electrode 521which transmits visible light, an EL layer 523, and the second electrode525. Furthermore, a partition 519 is formed so as to cover an endportion of the first electrode 521.

A light-emitting element 504 included in the light-emitting portion 551b has a top-emission structure and includes a first electrode 561, an ELlayer 563, and the second electrode 565 which transmits visible light.Furthermore, the partition 519 is formed so as to cover an end portionof the first electrode 561. In the EL layer 563, at least layers (e.g.,light-emitting layers) which contain different materials depending onthe light-emitting element are colored separately.

Over the support substrate 501, a lead wiring 517 for connecting anexternal input terminal through which a signal (e.g., a video signal, aclock signal, a start signal, or a reset signal) or a potential from theoutside is transmitted to the driver circuit portion 552 or 553 isprovided. Here, an example is described in which a flexible printedcircuit (FPC) 509 is provided as the external input terminal.

The driver circuit portions 552 and 553 include a plurality oftransistors. FIG. 3B illustrates two of the transistors in the drivercircuit portion 552 (transistors 542 and 543).

To prevent an increase in the number of manufacturing steps, the leadwiring 517 is preferably formed using the same material and the samestep(s) as those of the electrode or the wiring in the light-emittingportion or the driver circuit portion. Described in this embodiment isan example in which the lead wiring 517 is formed using the samematerial and the same step(s) as those of the source electrodes and thedrain electrodes of the transistors included in the light-emittingportion 551 and the driver circuit portion 552.

In FIG. 3B, the sealing material 507 is in contact with a firstinsulating layer 511 over the lead wiring 517. The adhesion of thesealing material 507 to metal is low in some cases. Therefore, thesealing material 507 is preferably in contact with an inorganicinsulating film over the lead wiring 517. Such a structure enables alight-emitting device to have high sealing capability, high adhesion,and high reliability. As examples of the inorganic insulating film,oxide films of metals and semiconductors, nitride films of metals andsemiconductors, and oxynitride films of metals and semiconductors aregiven, and specifically, a silicon oxide film, a silicon nitride film, asilicon oxynitride film, a silicon nitride oxide film, an aluminum oxidefilm, a titanium oxide film, and the like can be given.

The first insulating layer 511 has an effect of preventing diffusion ofimpurities into a semiconductor included in the transistor. As thesecond insulating layer 513, an insulating film having a planarizationfunction is preferably selected in order to reduce surface unevennessdue to the transistor.

There is no particular limitation on the structure and materials of thetransistor used in the light-emitting device of one embodiment of thepresent invention. A top-gate transistor may be used, or a bottom-gatetransistor such as an inverted staggered transistor may be used. Thetransistor may be a channel-etched transistor or a channel-protectivetransistor. An n-channel transistor may be used and a p-channeltransistor may also be used.

A semiconductor layer can be formed using silicon, an oxidesemiconductor, or an organic semiconductor. It is preferable that thetransistor be formed using an oxide semiconductor which is anIn—Ga—Zn-based metal oxide for a semiconductor layer so as to have lowoff-state current because an off-state leakage current of thelight-emitting element can be reduced.

The sealing substrate 505 illustrated in FIG. 3B is provided with acolor filter 533 as a coloring layer at a position overlapping with thelight-emitting element 503 (a light-emitting region thereof), and isalso provided with a black matrix 531 at a position overlapping with thepartition 519. Furthermore, an overcoat layer 535 is provided so as tocover the color filter 533 and the black matrix 531. The sealingsubstrate 505 illustrated in FIG. 3C is provided with a desiccant 506.

This embodiment can be combined with any other embodiment asappropriate.

Embodiment 4

In this embodiment, examples of electronic devices and lighting devicesof embodiments of the present invention will be described with referenceto FIGS. 4A to 4E and FIGS. 6A and 6B.

Electronic devices of this embodiment each include the light-emittingdevice of one embodiment of the present invention in a display portion.Lighting devices of this embodiment each include the light-emittingdevice of one embodiment of the present invention in a light-emittingportion (a lighting portion). Highly reliable electronic devices andhighly reliable lighting devices can be provided by adopting thelight-emitting device of one embodiment of the present invention.

Note that one embodiment of the present invention is not limited tothese examples, and the light-emitting device of one embodiment of thepresent invention is not necessarily included.

Examples of electronic devices to which the light-emitting device isapplied are television devices (also referred to as TV or televisionreceivers), monitors for computers and the like, cameras such as digitalcameras and digital video cameras, digital photo frames, cellular phones(also referred to as mobile phones or portable telephone devices),portable game machines, portable information terminals, audio playbackdevices, large game machines such as pin-ball machines, and the like.Specific examples of these electronic devices and lighting devices areillustrated in FIGS. 4A to 4E and FIGS. 6A and 6B.

The electronic device and lighting device of embodiments of the presentinvention may have flexibility. The electronic device and lightingdevice can be incorporated along a curved inside/outside wall surface ofa house or a building or a curved interior/exterior surface of a car.

FIG. 4A illustrates an example of a television device. In a televisiondevice 7100, a display portion 7102 is incorporated in a housing 7101.The display portion 7102 is capable of displaying images. Thelight-emitting device of one embodiment of the present invention can beused for the display portion 7102. In addition, here, the housing 7101is supported by a stand 7103.

The television device 7100 can be operated with an operation switchprovided in the housing 7101 or a separate remote controller 7111. Withoperation keys of the remote controller 7111, channels and volume can becontrolled and images displayed on the display portion 7102 can becontrolled. The remote controller 7111 may be provided with a displayportion for displaying data output from the remote controller 7111.

Note that the television device 7100 is provided with a receiver, amodem, and the like. With the use of the receiver, general televisionbroadcasting can be received. Moreover, when the television device isconnected to a communication network with or without wires via themodem, one-way (from a sender to a receiver) or two-way (between asender and a receiver or between receivers) data communication can beperformed.

FIG. 4B illustrates an example of a computer. A computer 7200 includes amain body 7201, a housing 7202, a display portion 7203, a keyboard 7204,an external connection port 7205, a pointing device 7206, and the like.Note that this computer is manufactured by using the light-emittingdevice of one embodiment of the present invention for the displayportion 7203.

FIG. 4C illustrates an example of a portable game machine. A portablegame machine 7300 has two housings, a housing 7301 a and a housing 7301b, which are connected with a joint portion 7302 so that the portablegame machine can be opened or closed. The housing 7301 a incorporates adisplay portion 7303 a, and the housing 7301 b incorporates a displayportion 7303 b. In addition, the portable game machine illustrated inFIG. 4C includes a speaker portion 7304, a recording medium insertionportion 7305, an operation key 7306, a connection terminal 7307, asensor 7308 (a sensor having a function of measuring or sensing force,displacement, position, speed, acceleration, angular velocity,rotational frequency, distance, light, liquid, magnetism, temperature,chemical substance, sound, time, hardness, electric field, electriccurrent, voltage, electric power, radiation, flow rate, humidity,gradient, oscillation, odor, or infrared rays), an LED lamp, amicrophone, and the like. It is needless to say that the structure ofthe portable game machine is not limited to the above structure as longas the light-emitting device of one embodiment of the present inventionis used for at least either the display portion 7303 a or the displayportion 7303 b, or both, and may include other accessories asappropriate. The portable game machine illustrated in FIG. 4C has afunction of reading out a program or data stored in a recoding medium todisplay it on the display portion, and a function of sharing data withanother portable game machine by wireless communication. Note thatfunctions of the portable game machine illustrated in FIG. 4C are notlimited to them, and the portable game machine can have variousfunctions.

FIG. 4D illustrates an example of a cellular phone. A cellular phone7400 is provided with a display portion 7402 incorporated in a housing7401, an operation button 7403, an external connection port 7404, aspeaker 7405, a microphone 7406, and the like. Note that the cellularphone 7400 is manufactured by using the light-emitting device of oneembodiment of the present invention for the display portion 7402.

When the display portion 7402 of the cellular phone 7400 illustrated inFIG. 4D is touched with a finger or the like, data can be input into thecellular phone. Furthermore, operations such as making a call andcreating e-mail can be performed by touching the display portion 7402with a finger or the like.

There are mainly three screen modes of the display portion 7402. Thefirst mode is a display mode mainly for displaying an image. The secondmode is an input mode mainly for inputting data such as characters. Thethird mode is a display-and-input mode in which two modes of the displaymode and the input mode are combined.

For example, in the case of making a call or creating e-mail, a textinput mode mainly for inputting text is selected for the display portion7402 so that text displayed on the screen can be input.

When a sensing device including a sensor such as a gyroscope sensor oran acceleration sensor for detecting inclination is provided inside thecellular phone 7400, display on the screen of the display portion 7402can be automatically changed in direction by determining the orientationof the cellular phone 7400 (whether the cellular phone 7400 is placedhorizontally or vertically for a landscape mode or a portrait mode).

The screen modes are changed by touch on the display portion 7402 oroperation with the operation button 7403 of the housing 7401. The screenmodes can be switched depending on the kind of images displayed on thedisplay portion 7402. For example, when a signal of an image displayedon the display portion is a signal of moving image data, the screen modeis switched to the display mode. When the signal is a signal of textdata, the screen mode is switched to the input mode.

Moreover, in the input mode, a signal detected by an optical sensor inthe display portion 7402 can be detected, whereby the screen mode may becontrolled so as to be switched from the input mode to the display modein the case where input by touching the display portion 7402 is notperformed for a specified period.

The display portion 7402 may function as an image sensor. For example,an image of a palm print, a fingerprint, or the like is taken by touchon the display portion 7402 with the palm or the finger, wherebypersonal authentication can be performed. Furthermore, when a backlightor a sensing light source which emits near-infrared light is provided inthe display portion, an image of a finger vein, a palm vein, or the likecan be taken.

FIG. 4E illustrates an example of a foldable tablet terminal (in an openstate). A tablet terminal 7500 includes a housing 7501 a, a housing 7501b, a display portion 7502 a, and a display portion 7502 b. The housing7501 a and the housing 7501 b are connected by a hinge 7503 and can beopened and closed using the hinge 7503 as an axis. The housing 7501 aincludes a power switch 7504, operation keys 7505, a speaker 7506, andthe like. Note that the tablet terminal 7500 is manufactured by usingthe light-emitting device of one embodiment of the present invention foreither the display portion 7502 a or the display portion 7502 b, orboth.

Part of the display portion 7502 a or the display portion 7502 b can beused as a touch panel region, where data can be input by touchingdisplayed operation keys. For example, a keyboard can be displayed onthe entire region of the display portion 7502 a so that the displayportion 7502 a is used as a touch panel, and the display portion 7502 bcan be used as a display screen.

The electronic device of one embodiment of the present invention mayinclude an input/output device (also referred to as a touch panel) and asecondary battery. It is preferable that the secondary battery iscapable of being charged by contactless power transmission. Theinput/output device includes a display portion and an input portion. Forthe display portion, the light-emitting device of one embodiment of thepresent invention can be used. For the input portion, an input deviceincluding a sensor element or the like (also referred to as a touchsensor) can be used.

As examples of the secondary battery, a lithium ion secondary batterysuch as a lithium polymer battery (lithium ion polymer battery) using agel electrolyte, a nickel-hydride battery, a nickel-cadmium battery, anorganic radical battery, a lead-acid battery, an air secondary battery,a nickel-zinc battery, and a silver-zinc battery can be given.

The electronic device of one embodiment of the present invention mayinclude a touch panel and an antenna. When a signal is received by theantenna, the electronic device can display an image, data, or the likeon a display portion. When the electronic device includes a secondarybattery, the antenna may be used for contactless power transmission.

FIGS. 5A to 5C illustrate a foldable portable information terminal 310.FIG. 5A illustrates the portable information terminal 310 that isopened. FIG. 5B illustrates the portable information terminal 310 thatis being opened or being folded. FIG. 5C illustrates the portableinformation terminal 310 that is folded. The portable informationterminal 310 is highly portable when folded. When the portableinformation terminal 310 is opened, a seamless large display region ishighly browsable.

A display panel 312 is supported by three housings 315 joined togetherby hinges 313. By folding the portable information terminal 310 at aconnection portion between two housings 315 with the hinges 313, theportable information terminal 310 can be reversibly changed in shapefrom an opened state to a folded state. The light-emitting device (ordisplay device) of one embodiment of the present invention can be usedfor the display panel 312. For example, a display device that can bebent with a radius of curvature of greater than or equal to 1 mm andless than or equal to 150 mm can be used.

FIGS. 5D and 5E illustrate a foldable portable information terminal 320.FIG. 5D illustrates the portable information terminal 320 that is foldedso that a display portion 322 is on the outside. FIG. 5E illustrates theportable information terminal 320 that is folded so that the displayportion 322 is on the inside. When the portable information terminal 320is not used, the portable information terminal 320 is folded so that anon-display portion 325 faces the outside, whereby the display portion322 can be prevented from being contaminated or damaged. Thelight-emitting device (or display device) of one embodiment of thepresent invention can be used for the display portion 322.

FIG. 5F is a perspective view illustrating an external shape of theportable information terminal 330. FIG. 5G is a top view of the portableinformation terminal 330. FIG. 5H is a perspective view illustrating anexternal shape of a portable information terminal 340.

The portable information terminals 330 and 340 each function as, forexample, one or more of a telephone set, a notebook, and an informationbrowsing system. Specifically, the portable information terminals 330and 340 each can be used as a smartphone.

The portable information terminals 330 and 340 can display charactersand image data on its plurality of surfaces. For example, threeoperation buttons 339 can be displayed on one surface (FIGS. 5F and 5H).In addition, data 337 indicated by dashed rectangles can be displayed onanother surface (FIGS. 5G and 5H). Examples of the data 337 includenotification from a social networking service (SNS), display indicatingreception of e-mail or an incoming call, the title of e-mail or thelike, the sender of e-mail or the like, the date, the time, remainingbattery, and the reception strength of an antenna. Alternatively, theoperation buttons 339, an icon, or the like may be displayed in place ofthe data 337. Although FIGS. 5F and 5G illustrate an example in whichthe data 337 is displayed at the top, one embodiment of the presentinvention is not limited thereto. The data may be displayed, forexample, on the side as in the portable information terminal 340illustrated in FIG. 5H.

The light-emitting device (or display device) of one embodiment of thepresent invention can be used for a display portion 333 mounted in eachof a housing 335 of the portable information terminal 330 and a housing336 of the portable information terminal 340.

As in a portable information terminal 345 illustrated in FIG. SI, datamay be displayed on three or more surfaces. Here, data 355, data 356,and data 357 are displayed on different surfaces. The light-emittingdevice (or display device) of one embodiment of the present inventioncan be used for a display portion 358 included in a housing 351 of theportable information terminal 345.

An indoor lighting device 7601, a roll-type lighting device 7602, a desklamp 7603, and a planar lighting device 7604 illustrated in FIG. 6A areeach an example of a lighting device which includes the light-emittingdevice of one embodiment of the present invention. Since thelight-emitting device of one embodiment of the present invention canhave a larger area, it can be used as a large-area lighting device.Furthermore, since the light-emitting device is thin, the light-emittingdevice can be mounted on a wall.

A desk lamp illustrated in FIG. 6B includes a lighting portion 7701, asupport 7703, a support base 7705, and the like. The light-emittingdevice of one embodiment of the present invention is used for thelighting portion 7701. In one embodiment of the present invention, alighting device whose light-emitting portion has a curved surface or alighting device including a flexible lighting portion can be achieved.Such use of a flexible light-emitting device for a lighting deviceenables a place having a curved surface, such as the ceiling ordashboard of a motor vehicle, to be provided with the lighting device,as well as increases the degree of freedom in design of the lightingdevice. The lighting device of one embodiment of the present inventionmay include a housing or a cover.

This embodiment can be combined with any other embodiment asappropriate.

Example 1 Synthesis Example 1

This example describes a method for synthesizing2-[3′-(benzo[b]naphtho[2,3-d]furan-8-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline(abbreviation: 2mBnf(II)BPDBq), which is a compound of one embodiment ofthe present invention represented by Structural Formula (101). Thisexample also describes a method for synthesizing8-chlorobenzo[b]naphtho[2,3-d]furan, which is a compound of oneembodiment of the present invention represented by Structural Formula(201).

Step 1: Synthesis of 3-(3-Chloro-2-fluorophenyl)-2-naphthol

A synthesis scheme of Step 1 is shown in (B−1).

In a 1000 mL three-neck flask were put 16 g (70 mmol) of3-bromo-2-naphthol, 12 g (70 mmol) of 3-chloro-2-fluorobenzeneboronicacid, and 1.1 g (3.5 mol) of tri(ortho-tolyl)phosphine, and the air inthe flask was replaced with nitrogen. To this mixture, 300 mL oftoluene, 60 mL of ethanol, and 90 mL of an aqueous solution of potassiumcarbonate (2.0 mol/L) were added. The mixture was degassed by beingstirred while the pressure in the flask was reduced; then, the air inthe flask was replaced with nitrogen. To this mixture was added 0.16 g(0.70 mmol) of palladium(II) acetate, and the resulting mixture wasstirred at 80° C. under a nitrogen stream for 3 hours. After thestirring, the organic layer of the mixture was washed with water and theaqueous layer was then subjected to extraction with ethyl acetate. Thesolution of the extract combined with the organic layer was washed withsaturated brine, and the organic layer was dried with magnesium sulfate.The resulting mixture was gravity-filtered, and the resulting filtratewas concentrated to give 23 g of a brown liquid that contains a targetsubstance as a main component.

Step 2: Synthesis of 8-Chlorobenzo[b]naphtho[2,3-d]furan

A synthesis scheme of Step 2 is shown in (B-2).

Into a 500 mL recovery flask were put 23 g of the brown liquid obtainedin Step 1, 300 mL of N-methyl-2-pyrrolidone, and 27 g (0.20 mol) ofpotassium carbonate, and the mixture was stirred at 150° C. in the airfor 7 hours. After the stirring, approximately 50 mL of water andapproximately 50 mL of hydrochloric acid (1.0 mol/L) were added to theresulting mixture. To the resulting solution was added approximately 100mL of ethyl acetate; then, the aqueous layer was subjected to extractionwith ethyl acetate three times. The solution of the extract combinedwith the organic layer was washed with a saturated aqueous solution ofsodium hydrogen carbonate and saturated brine, and magnesium sulfate wasthen added. The mixture was gravity-filtered, and the resulting filtratewas concentrated to give 5.4 g of a pale brown solid of a targetsubstance in a yield of 23% (this yield is the total of Step 1 and Step2).

¹H NMR data of the pale brown solid are as follows:

¹H NMR (CDCl₃, 500 MHz): δ=7.32 (t, J=7.5 Hz, 1H), 7.49-7.57 (m, 3H),7.96 (dd, J1=8.25 Hz, 12=1.5 Hz, 1H), 8.00 (d, J=9.0 Hz, 1H), 8.01 (s,1H), 8.04 (d, J=9.0 Hz, 1H), 8.42 (s, 1H).

In addition, FIGS. 7A and 7B show ¹H NMR charts. Note that FIG. 7B is achart showing an enlarged part of FIG. 7A in the range of 7.00 ppm to9.00 ppm.

Step 3: Synthesis of2-(Benzo[b]naphtho[2,3-d]furan-8-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane

A synthesis scheme of Step 3 is shown in (B-3).

In a 200 mL three-neck flask were put 1.1 g (4.3 mmol) of8-chlorobenzo[b]naphtho[2,3-d]furan, 1.1 g (4.3 mmol) ofbis(pinacolato)diboron, 0.79 g (8.0 mmol) of potassium acetate, and 179mg of (0.50 mmol) of di(1-adamantyl)-n-butylphosphine, and the air inthe flask was replaced with nitrogen. To this mixture, 25 mL of1,4-dioxane was added. The mixture was degassed by being stirred whilethe pressure in the flask was reduced; then, the air in the flask wasreplaced with nitrogen. To this mixture was added 81 mg (0.11 mmol) of[1,1′-bis(diphenylphosphino)ferrocene]palladium(II) dichloridedichloromethane adduct, and the mixture was refluxed at 180° C. under anitrogen stream for 5 hours. After the reflux, a thin-layer silica gelchromatography (a developing solvent of hexane:ethyl acetate=10:1) wasperformed to check on the progress of the reaction. Because no spotderived from the raw materials was observed, the next reaction was thenperformed.

Step 4: Synthesis of 2mBnf(II)BPDBq

A synthesis scheme of Step 4 is shown in (B-4).

After Step 3, the following reaction was carried out in the samecontainer without work-up (posttreatment). To the reaction mixtureobtained in Step 3 and containing2-(benzo[b]naphtho[2,3-d]furan-8-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane,1.9 g (4.3 mmol) of 2-(3′-bromobiphenyl-3-yl)dibenzo[f,h]quinoxaline and3.3 g (10 mmol) of cesium carbonate were added. To this mixture, 0.12 mg(0.10 mol) of tetrakis(triphenylphosphine)palladium(0) was added, andthe mixture was stirred at 150° C. under a nitrogen stream for 5.5hours. To the resulting mixture, approximately 100 mL of toluene wasadded, and this mixture was refluxed. After the reflux, a solidremaining unsolved was collected by suction-filtration, and theresulting solid was washed with water and ethanol in this order to give1.4 g of a pale brown solid in a crude yield of 55%.

By a train sublimation method, 1.4 g of the obtained pale brown solidwas purified. In the sublimation purification, the solid was heated at330° C. for 15 hours under a pressure of 2.5 Pa with a flow rate ofargon gas of 15 mL/min. After the sublimation purification, 0.96 g of apale yellow solid was obtained at a collection rate of 69%.

This compound was identified as 2mBnf(II)BPDBq, which was the targetsubstance, by nuclear magnetic resonance (NMR) spectroscopy.

¹H NMR data of the brown solid are as follows: ¹H NMR(tetrschloroethane-d₂, 500 MHz): δ=7.49-7.55 (m, 3H), 7.73-7.87 (m, 8H),7.90-7.94 (m, 2H), 8.00 (s, 1H), 8.04 (d, J=7.5 Hz, 1H), 8.07 (d, J=7.5Hz, 1H), 8.12 (d, J=8.5 Hz, 1H), 8.37-8.39 (m, 2H), 8.48 (s, 1H), 8.67(d, J=8.0 Hz, 2H), 8.74 (s, 1H), 9.31 (d, J=8.0 Hz, 1H), 9.47 (d, J=8.0Hz, 1H), 9.53 (s, 1H).

In addition, FIGS. 8A and 8B show ¹H NMR charts. Note that FIG. 8B is achart showing an enlarged part of FIG. 8A in the range of 7.00 ppm to10.0 ppm.

Furthermore, FIG. 9A shows an absorption spectrum of a toluene solutionof 2mBnf(II)BPDBq, and FIG. 9B shows an emission spectrum thereof. FIG.10A shows an absorption spectrum of a thin film of 2mBnf(II)BPDBq andFIG. 10B shows an emission spectrum thereof. The absorption spectrum wasmeasured using an ultraviolet-visible spectrophotometer (V-550, producedby JASCO Corporation). For the measurement, the solution was put in aquartz cell and the thin film was formed on a quartz substrate byevaporation. The absorption spectrum of the solution was obtained bysubtracting the absorption spectra of the quartz cell and toluene fromthose of the quartz cell and the solution, and the absorption spectrumof the thin film was obtained by subtracting the absorption spectrum ofthe quartz substrate from the absorption spectra of the thin film on thequartz substrate. In FIGS. 9A and 9B and FIGS. 10A and 10B, thehorizontal axis indicates wavelength (nm) and the vertical axisindicates intensity (arbitrary unit). In the case of the toluenesolution, absorption peaks are observed around 280 nm, 310 nm, 322 nm,340 nm, and 358 nm, and emission wavelength peaks are observed at 385 nmand 404 nm (excitation wavelength: 358 nm). In the case of the thinfilm, absorption peaks are observed around 258 nm, 315 nm, 327 nm, 346nm, 365 nm, and 384 nm, and an emission wavelength peak is observed at435 nm (excitation wavelength: 369 nm).

Further, a HOMO level and a LUMO level of 2mBnf(II)BPDBq were obtainedby cyclic voltammetry (CV) measurement. An electrochemical analyzer (ALSmodel 600A or 600C, produced by BAS Inc.) was used for the CVmeasurement.

As for a solution used for the CV measurement, dehydrateddimethylformamide (DMF, produced by Sigma-Aldrich Co. LLC., 99.8%,catalog No. 22705-6) was used as a solvent, and tetra-n-butylammoniumperchlorate (n-Bu₄NClO₄, produced by Tokyo Chemical Industry Co., Ltd.,catalog No. T0836), which was a supporting electrolyte, was dissolved inthe solvent such that the concentration of tetra-n-butylammoniumperchlorate was 100 mmol/L. Furthermore, the object to be measured wasdissolved in the solution such that the concentration was 2 mmol/L. Aplatinum electrode (PTE platinum electrode, produced by BAS Inc.) wasused as a working electrode, a platinum electrode (Pt counter electrodefor VC-3 (5 cm), produced by BAS Inc.) was used as an auxiliaryelectrode, and an Ag/Ag′ electrode (RE-7 reference electrode fornonaqueous solvent, produced by BAS Inc.) was used as a referenceelectrode. Note that the measurement was conducted at room temperature(20° C. to 25° C.). In addition, the scan rate at the CV measurement wasset to 0.1 V/sec. Note that the potential energy of the referenceelectrode with respect to the vacuum level was assumed to be −4.94 [eV]in this example.

On the assumption that the intermediate potential (the half-wavepotential) between the oxidation peak potential E_(pa) and the reductionpeak potential E_(pe) which are obtained in the CV measurementcorresponds to the HOMO level, the HOMO level of 2mBnf(II)BPDBq wascalculated to be −6.03 eV, and the LUMO level of 2mBnf(II)BPDBq wascalculated to be −2.95 eV. Accordingly, the band gap (ΔE) of2mBnf(II)BPDBq was found to be 3.08 eV.

Furthermore, 2mBnf(II)BPDBq was subjected to mass spectrometric (MS)analysis by liquid chromatography mass spectrometry (LC-MS).

In the analysis by LC-MS, liquid chromatography (LC) separation wascarried out with UltiMate 3000 produced by Thermo Fisher ScientificK.K., and the MS analysis was carried out with Q Exactive produced byThermo Fisher Scientific K.K. ACQUITY UPLC BEH C8 (2.1×100 mm, 1.7 μm)was used as a column for the LC separation, and the column temperaturewas 40° C. Acetonitrile was used for Mobile Phase A and a 0.1% aqueoussolution of formic acid was used for Mobile Phase B. Analysis wasperformed by a gradient method for 10 minutes, in which the proportionof acetonitrile was 70% at the start of the analysis and increasedlinearly to reach 95% after 10 minutes from the start of the analysis. Asample was prepared in such a manner that 2mBnf(II)BPDBq was dissolvedin chloroform at a given concentration and the mixture was diluted withacetonitrile. The injection amount was 5.0 μL.

In the MS analysis, ionization was carried out by an electrosprayionization (ESI) method, and measurement was carried out bytargeted-MS². Conditions of an ion source were set as follows: the flowrates of a sheath gas, an Aux gas, and a Sweep gas were 50, 10, and 0,respectively, the spray voltage was 3.5 kV, the capillary temperaturewas 380° C., the S lens voltage was 55.0, and the HESI heatertemperature was 350° C. The resolution was 35000, the AGC target was3e6, the mass range was m/z=50.00 to 630.00, and the detection wasperformed in a positive mode.

A component with m/z of 599.21±10 ppm that underwent the ionizationunder the above-described conditions was collided with an argon gas in acollision cell to dissociate into product ions, and MS/MS measurementwas carried out. Ions which were generated under a normalized collisionenergy (NCE) for the collision with argon of 50 were detected with aFourier transform mass spectrometer (FT MS). FIGS. 11A and 11B show themeasurement results.

The results in FIGS. 11A and 11B demonstrate that product ions of2mBnf(II)BPDBq are detected around m/z=381, m/z=229, and m/z=220. Notethat the results in FIGS. 11A and 11B show characteristics derived from2mBnf(II)BPDBq and thus can be regarded as important data foridentifying 2mBnf(II)BPDBq contained in a mixture.

The product ion around m/z=381 is presumed to be a cation derived from2-(3,1′-biphenyl-1-yl)dibenzo[f,h]quinoxaline in 2mBnf(II)BPDBq, andindicates a partial structure of the compound of one embodiment of thepresent invention. The product ion around m/z=229 is presumed to be acation derived from dibenzo[f,h]quinoxaline in 2mBnf(II)BPDBq, andindicates a partial structure of the compound of one embodiment of thepresent invention. The product ion around m/z=220 is presumed to be acation derived from an alcohol formed by cleavage of an ether linkage inbenzo[b]naphtho[2,3-d]furan (Structural Formula (10) or StructuralFormula (11)), and indicates a partial structure of the compound of oneembodiment of the present invention.

The product ion around m/z=572 is presumed to be a cation derived from2mBnf(II)BPDBq in the state where one CH and one N are dissociated fromdibenzo[f,h]quinoxaline in 2mBnf(II)BPDBq, and indicates a partialstructure of the compound of one embodiment of the present invention. Inparticular, this is one of features of the compound of one embodiment ofthe present invention in which a substituent (in 2mBnf(II)BPDBq, abiphenyl skeleton bonded to a benzo[b]naphtho[2,3-d]furan skeleton) isbonded to the 2-position of dibenzo[f,h]quinoxaline.

Phosphorescence of 2mBnf(II)BPDBq was measured.

An evaporated film of 2mBnf(II)BPDBq was formed and was subjected tolow-temperature photoluminescence (PL) measurement. The measurement wasperformed by using a PL microscope, LabRAM HR-PL, produced by HORIBA,Ltd., a He—Cd laser (325 nm) as excitation light, and a CCD detector ata measurement temperature of 10 K.

For the measurement, the evaporated film was formed over a quartzsubstrate to a thickness of 50 nm and another quartz substrate wasattached to the deposition surface in a nitrogen atmosphere.

According to the measurement results, a peak wavelength on the shortestwavelength side of the phosphorescence spectrum was 536 nm. The T₁ levelof 2mBnf(II)BPDBq was estimated from the wavelength to be 2.31 eV.

It was found that aggregation of the thin film of 2mBnf(II)BPDBq is noteasily caused even under the air and the thin film suffers only a smallchange in shape and has high film quality.

The decomposition temperature Td of 2mBnf(II)BPDBq under atmosphericpressure was measured by thermogravimetry-differential thermal analysis(TG-DTA) to be 500° C. or more, which means that 2mBnf(II)BPDBq has highheat resistance. The measurement was conducted by using a high vacuumdifferential type differential thermal balance (TG/DTA 2410SA, producedby Bruker AXS K.K.).

Furthermore, thermophysical properties were measured using adifferential scanning calorimeter (Pyris 1 DSC, produced by PerkinElmerInc.). One cycle in the measurement was as follows: a sample wasmaintained at −10° C. for 1 minute, the temperature was raised from −10°C. to 350° C. at a rate of 50° C./min, the sample was maintained at 350°C. for 1 minute, and the temperature was lowered from 350° C. to −10° C.at a rate of 50° C./min. In this measurement, two cycles were performedand the thermophysical properties were measured from the data obtainedin the second cycle. Thus, the glass transition temperature Tg of2mBnf(II)BPDBq was found to be 119° C., the crystallization temperatureTc thereof was found to be 206° C., and the melting points Tm thereofwere found to be 285° C. and 300° C. Accordingly, 2mBnf(II)BPDBq has ahigh glass transition temperature, a high melting point, a highdecomposition temperature, and high heat resistance.

Example 2

In this example, the light-emitting element of one embodiment of thepresent invention will be described with reference to FIG. 12. Chemicalformulae of materials used in this example are shown below. Note thatthe chemical formulae of the materials which are shown above areomitted.

A method for fabricating a light-emitting element 1 of this example willbe described below.

(Light-Emitting Element 1)

A film of indium tin oxide containing silicon (ITSO) was formed over aglass substrate 1100 by a sputtering method, so that a first electrode1101 which functions as an anode was formed. The thickness thereof was110 nm and the electrode area was 2 mm×2 mm.

Next, as pretreatment for forming the light-emitting element over theglass substrate 1100, UV-ozone treatment was performed for 370 secondsafter washing of a surface of the glass substrate 1100 with water andbaking that was performed at 200° C. for 1 hour.

After that, the glass substrate 1100 was transferred into a vacuumevaporation apparatus where the pressure had been reduced toapproximately 10⁻⁴ Pa, and was subjected to vacuum baking at 170° C. for30 minutes in a heating chamber of the vacuum evaporation apparatus, andthen the glass substrate 1100 was cooled down for approximately 30minutes.

Then, the glass substrate 1100 over which the first electrode 1101 wasformed was fixed to a substrate holder provided in the vacuumevaporation apparatus so that the surface on which the first electrode1101 was formed faced downward. The pressure in the vacuum evaporationapparatus was reduced to approximately 10⁻⁴ Pa. After that, over thefirst electrode 1101, 4,4′,4″-(1,3,5-benzenetriyl)tri(dibenzothiophene)(abbreviation: DBT3P-II) and molybdenum(VI) oxide were deposited byco-evaporation, so that a hole-injection layer 1111 was formed. Thethickness of the hole-injection layer 1111 was set to 20 nm, and theweight ratio of DBT3P-II to molybdenum oxide was adjusted to 4:2(=DBT3P-II: molybdenum oxide). Note that the co-evaporation methodrefers to an evaporation method in which evaporation is carried out froma plurality of evaporation sources at the same time in one treatmentchamber.

Next, a film of 4-phenyl-4′-(9-phenylfluorene-9-yl)triphenylamine(abbreviation: BPAFLP) was formed to a thickness of 20 nm over thehole-injection layer 1111 to form a hole-transport layer 1112.

Furthermore, a light-emitting layer 1113 was formed over thehole-transport layer 1112 by co-evaporation of 2mBnf(II)BPDBq,N-(1,1′-biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9H-fluoren-2-amine(abbreviation: PCBBiF), and(acetylacetonato)bis(4,6-diphenylpyrimidinato)iridium(III)(abbreviation: [Ir(dppm)₂(acac)]). Here, a 20-nm-thick layer which wasformed with the weight ratio of 2mBnf(II)BPDBq to PCBBiF to[Ir(dppm)₂(acac)] adjusted to 0.7:0.3:0.05(=2mBnf(II)BPDBq:PCBBiF:[Ir(dppm)₂(acac)]) and a 20-nm-thick layer whichwas formed with the weight ratio adjusted to 0.8:0.2:0.05(=2mBnf(II)BPDBq:PCBBiF:[Ir(dppm)₂(acac)]) were stacked.

Next, a film of 2mBnf(II)BPDBq was formed to a thickness of 20 nm overthe light-emitting layer 1113 and then a film of bathophenanthroline(abbreviation: BPhen) was formed to a thickness of 10 nm, so that anelectron-transport layer 1114 was formed.

After that, over the electron-transport layer 1114, a film of lithiumfluoride (LiF) was formed by evaporation to a thickness of 1 nm to forman electron-injection layer 1115.

Lastly, aluminum was deposited by evaporation to a thickness of 200 nmto form a second electrode 1103 functioning as a cathode. Thus, thelight-emitting element 1 of this example was fabricated.

Note that in all the above evaporation steps, evaporation was performedby a resistance-heating method.

Table 1 shows the element structure of the light-emitting elementfabricated as described above in this example.

TABLE 1 Hole- Hole- Electron- First injection transport injection Secondelectrode layer layer Light-emitting layer Electron-transport layerlayer electrode Light- ITSO DBT3P-II: BPAFLP 2mBnf(II)BPDBq:PCBBiF:2mBnf(II)BPDBq BPhen LiF Al emitting 110 nm MoO_(x) 20 nm[Ir(dppm)₂(acac)] 20 nm 10 nm 1 nm 200 nm element (=4:2) (=0.7:0.3:0.05)(=0.8:0.2:0.05) 1 20 nm 20 nm 20 nm

The light-emitting element of this example was sealed in a glove boxunder a nitrogen atmosphere so as not to be exposed to the air. Then,the operation characteristics of the light-emitting element weremeasured. Note that the measurement was carried out at room temperature(in an atmosphere kept at 25° C.).

FIG. 13 shows voltage-luminance characteristics of the light-emittingelement 1. In FIG. 13, the horizontal axis indicates voltage (V), andthe vertical axis indicates luminance (cd/m²). FIG. 14 showsluminance-current efficiency characteristics. In FIG. 14, the horizontalaxis indicates luminance (cd/m²) and the vertical axis indicates currentefficiency (cd/A). FIG. 15 shows voltage-current characteristics. InFIG. 15, the horizontal axis indicates voltage (V) and the vertical axisindicates current (mA). FIG. 16 shows an emission spectrum of thelight-emitting element 1. In FIG. 16, the horizontal axis indicates awavelength (nm) and the vertical axis indicates emission intensity(arbitrary unit). Table 2 shows the voltage (V), current density(mA/cm²), CIE chromaticity coordinates (x, y), current efficiency(cd/A), power efficiency (lm/W), and external quantum efficiency (%) ofthe light-emitting element 1 at a luminance of 900 cd/m².

TABLE 2 External Current Current Power quantum Voltage density Luminanceefficiency efficiency efficiency (V) (mA/cm²) Chromaticity xChromaticity y (cd/m)² (cd/A) (lm/W) (%) Light- 3.3 1.3 0.57 0.43 900 6966 29 emitting element 1

The CIE chromaticity coordinates (x, y) at a luminance of 900 cd/m² ofthe light-emitting element 1 were (0.57, 0.43) and the light-emittingelement 1 exhibited orange light emission. These results show thatorange light emission originating from [Ir(dppm)₂(acac)] was providedfrom the light-emitting element 1.

The measurement results of the operation characteristics show that thelight-emitting element 1 has high emission efficiency and a low drivevoltage.

A reliability test of the light-emitting element 1 was conducted. FIG.17 shows results of the reliability test. In FIG. 17, the vertical axisindicates normalized luminance (%) with an initial luminance of 100% andthe horizontal axis indicates driving time (h) of the element. In thereliability test, which was conducted at room temperature, thelight-emitting element 1 was driven under the conditions where theinitial luminance was set to 5000 cd/m² and the current density wasconstant. FIG. 17 shows that the light-emitting element 1 kept 91% ofthe initial luminance after 1300 hours. The results of the reliabilitytest show that the light-emitting element 1 has a long lifetime.

Example 3

In this example, the light-emitting element of one embodiment of thepresent invention was fabricated and a preservation test was conducted.The results of the preservation test are described. A chemical formulaof a material used in this example is shown below. Note that thechemical formulae of the materials which are shown above are omitted.

A method for fabricating a light-emitting element 2 of this example willbe described below. FIG. 12 can be referred to for the structure of thelight-emitting element in this example.

(Light-Emitting Element 2)

In the light-emitting element 2, components other than thelight-emitting layer 1113 were formed in the same manners as those ofthe light-emitting element 1. Here, only the step different from that inthe method for fabricating the light-emitting element 1 is described.

The light-emitting layer 1113 of the light-emitting element 2 was formedby co-evaporation of 2mBnf(II)BPDBq, PCBBiF, and(acetylacetonato)bis(6-tert-butyl-4-phenylpyrimidinato)iridium(III)(abbreviation: [Ir(tBuppm)₂(acac)]). Here, a 20-nm-thick layer which wasformed with the weight ratio of 2mBnf(II)BPDBq to PCBBiF to[Ir(tBuppm)₂(acac)] adjusted to 0.7:0.3:0.05(=2mBnf(II)BPDBq:PCBBiF:[Ir(tBuppm)₂(acac)]) and a 20-nm-thick layerwhich was formed with the weight ratio adjusted to 0.8:0.2:0.05(=2mBnf(II)BPDBq:PCBBiF:[Ir(tBuppm)₂(acac)]) were stacked.

Table 3 shows the element structure of the light-emitting elementfabricated as described above in this example.

TABLE 3 Hole- Hole- Electron- First injection transport injection Secondelectrode layer layer Light-emitting layer Electron-transport layerlayer electrode Light- ITSO DBT3P-II: BPAFLP 2mBnf(II)BPDBq:PCBBiF:2mBnf(II)BPDBq BPhen LiF Al emitting 110 nm MoO_(x) 20 nm[Ir(tBuppm)₂(acac)] 20 nm 10 nm 1 nm 200 nm element (=4:2)(=0.7:0.3:0.05) (=0.8:0.2:0.05) 2 20 nm 20 nm 20 nm

In this example, the fabricated light-emitting element was preserved ina thermostatic oven maintained at 100° C., and after a predeterminedtime elapsed, the operation characteristics were measured. Note that theoperation characteristics were measured at room temperature (in anatmosphere kept at 25° C.) after the light-emitting element was takenout of the thermostatic oven.

FIG. 18 shows the voltage-current characteristics of the light-emittingelement after preservation at 100° C. for 200 hours, and FIG. 19 showsthe luminance-external quantum efficiency characteristics thereof. Notethat FIGS. 18 and 19 also show the characteristics of the light-emittingelement before the preservation test, those after 25-hour preservation,and those after 50-hour preservation.

As can be seen in FIGS. 18 and 19, the light-emitting element in thisexample suffered only a small change in the voltage-currentcharacteristics and luminance-external quantum efficiencycharacteristics even after preservation at 100° C. for 200 hours, andthe element characteristics hardly deteriorated. Accordingly, with theuse of the compound of one embodiment of the present invention, a highlyheat-resistant and highly reliable light-emitting element can beobtained.

This application is based on Japanese Patent Application serial no.2014-095159 filed with the Japan Patent Office on May 2, 2014, theentire contents of which are hereby incorporated by reference.

What is claimed is:
 1. A compound represented by Formula (G0):A¹-Ar-A²  (G0) wherein: A¹ represents a dibenzo[f,h]quinoxalinyl group;A² represents a benzo[b]naphtho[2,3-d]furanyl group; Ar represents anarylene group having 6 to 25 carbon atoms; and thedibenzo[f,h]quinoxalinyl group, the benzo[b]naphtho[2,3-d]furanyl group,and the arylene group are separately unsubstituted or substituted by anyone of an alkyl group having 1 to 6 carbon atoms, a cycloalkyl grouphaving 3 to 6 carbon atoms, and an aryl group having 6 to 13 carbonatoms.
 2. The compound according to claim 1, wherein: the compound isrepresented by Formula (G1);

one of R⁷ to R¹⁰ represents a substituent represented by Formula (G1-1);and R¹ to R⁶ and the others of R⁷ to R¹⁰ separately represent any one ofhydrogen, an alkyl group having 1 to 6 carbon atoms, a cycloalkyl grouphaving 3 to 6 carbon atoms, and an aryl group having 6 to 13 carbonatoms.
 3. The compound according to claim 2, wherein: the compound isrepresented by Formula (G2).


4. A light-emitting element comprising, between a pair of electrodes, alayer containing the compound according to claim
 1. 5. A light-emittingdevice comprising: the light-emitting element according to claim 4; anda transistor or a substrate.
 6. An electronic device comprising: thelight-emitting device according to claim 5; and a microphone, a speaker,or an external connection terminal.
 7. A lighting device comprising: thelight-emitting device according to claim 5; and a support, a housing, ora cover.
 8. A compound represented by Formula (G3):

wherein: R¹ to R⁹ and R¹¹ to R¹⁹ separately represent any one ofhydrogen, an alkyl group having 1 to 6 carbon atoms, a cycloalkyl grouphaving 3 to 6 carbon atoms, and an aryl group having 6 to 13 carbonatoms; Ar represents an arylene group having 6 to 25 carbon atoms; andthe aryl group and the arylene group are separately unsubstituted orsubstituted by any one of an alkyl group having 1 to 6 carbon atoms, acycloalkyl group having 3 to 6 carbon atoms, and an aryl group having 6to 13 carbon atoms.
 9. The compound according to claim 8, wherein thecompound is represented by Formula (101).


10. A light-emitting element comprising, between a pair of electrodes, alayer containing the compound according to claim
 8. 11. A light-emittingdevice comprising: the light-emitting element according to claim 10; anda transistor or a substrate.
 12. An electronic device comprising: thelight-emitting device according to claim 11; and a microphone, aspeaker, or an external connection terminal.
 13. A lighting devicecomprising: the light-emitting device according to claim 11; and asupport, a housing, or a cover.
 14. A light-emitting element comprising,between a pair of electrodes, a layer containing a compound, wherein thecompound comprises a dibenzo[f,h]quinoxaline skeleton and abenzo[b]naphtho[2,3-d]furan skeleton.
 15. The light-emitting elementaccording to claim 14, wherein the dibenzo[f,h]quinoxaline skeleton andthe benzo[b]naphtho[2,3-d]furan skeleton are bonded through an aryleneskeleton.
 16. A light-emitting device comprising: the light-emittingelement according to claim 15; and a transistor or a substrate.
 17. Anelectronic device comprising: the light-emitting device according toclaim 16; and a microphone, a speaker, or an external connectionterminal.
 18. A lighting device comprising: the light-emitting deviceaccording to claim 16; and a support, a housing, or a cover.